24hxi Glow worm boiler with Honeywell Y plan - Going to F1

I have an 18 month old 24hxi Glow worm boiler configured with a
Honeywell 3 port valve, Llandis control panel, Honeywell wall
thermostat and Honeywell cylinder thermostat. The system is configured
as the Honeywell Y plan, and can supply hot water only, heating only
or hot water and heating combined. It is a conventional system, not a
Whilst under warranty (Year 1) the system kept dropping to F1 (fail to
ignite) at apparently random times. A Glow worm engineer called and
told me that there had been a fault with some of these models due to
some spade terminals being poorly fitted. He re-crimped the terminals
and all seemed OK.
The fault recurred very occasionally after this, but not sufficient to
justify a call-out.
The only change from standard that I have done since then is to change
the 3 terminal(+earth) - (with accellerate) Honeywell wall stat to a
two wire programmable stat. I jumpered a wire from the Live terminal
to terminal 4 in the panel behind the system programmer as per
Honeywell's instructions for upgrading a T6360 wall thermostat to a 2
wire programmable.
The system happily supplied HW throughout this summer, but when we
started requiring HW+Heating combined a few random F1s started to
appear. More recently we got an F4, and our installer called,
struggled to find a solution, but after a call to Glow worm he flicked
a switch near top left of boiler, and the F4 disappeared. The
installer seemed to think that this was just a random fault.
All seemed fine until we started to leave the heating and HW on in the
night, when we began to wake to a flashing F1 again.
I have replaced the 3 port valve, the wall thermostat, the cylinder
thermostat with identical but new items in the hope that this would
fix things, but the dreaded F1s continue.
I have swapped back the original wall stat and removed the link, but
the same problem persists.
Today - a partial breakthrough. The systems fails to F1 when there is
still a demand for heat (via the wall thermostat) but the cylinder
stat decides the cylinder is up to temp and switches off.
The 3 port valve correctly positions for HW only, both HW and CH, AND
CH only.
I guess that the night period with low consumption of hot water allows
sufficient time for the H/W thermostat to cut out, thus causing the
F1, but I have no knowledge of why this might happen and a way to
resolve things.
The system is quite happy to run in Hw only mode or CH only mode, or
combined mode until the cylinder stat switches off.
I really would appreciate some advice. The only good news is that with
the boiler etc downstairs and the cylinder etc upstairs I have
probably exercised sufficiently today to allow me to eat the entire
turkey myself this year! :>))
Reply to
In an earlier contribution to this discussion,
When you get the F1 error, what do you have to do to get the boiler to start up again?
Are you sure that F1 is the *only* error? According to the fault-finding section in the installation manual (which you can download from
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if you don't have one) you may get several errors at the same time, and can scroll through the error memory to see them all.
I have a hunch that there may be an F5 lurking there somewhere - indicating that the boiler has overheated - particularly if you have to press the reset button to re-start it. This could possibly happen when the only demand is for CH, if you've got TRVs on all or virtually all rads, and they are all closed because the house is warm enough. If the boiler is going full chat to heat both HW and CH, and the HW demand is suddenly satisfied, causing the valve to move to the CH-only position, there may be insufficient flow through the boiler to carry away the residual heat - so it may overheat even after it has stopped firing.
*Do* you have any way of ensuring that there is always a decent flow path for the water - either with an automatic by-pass valve, or by having one largish radiator which cannot be turned off (i.e. with lockshields both ends, and no TRV)?
Reply to
Roger Mills
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if you don't have one) you may get several errors at the same time, and can
I just have to switch off the boiler with the switch on the front, or by switching off the mains power to the programmer.
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if you don't have one) you may get several errors at the same time, and can
Thanks for the link. I do have Instructions for use/Installation & Servicing, BUT the linked PDF gives more detail. I will study it tomorrow and search for more errors.
Will check this tomorrow. Tonight as a test I have set the stat on the cylinder very high (and above that of the boiler) so that the water heating will not switch off. It will be interesting to see if there is an F1 in the morning.
I do have TRVs, and also 2 rads (both doubles 1 large & 1 small) which have lockshields full on, but tomorrow night I will leave more rad stats on full as a test for overheating.
Just one more observation. If I manually switch off the cylinder thermostat whilst the heating is on, the pump stops, and then within 10 seconds the F1 flashes. There seems no time for the boiler to overheat and no kettling effect that I think might expect.
THANKS very much for the ideas, I will feedback asap.
Reply to
In an earlier contribution to this discussion,
It's worrying if the pump stops dead. Are you sure that the pump is correctly connected - it needs to be wired into the boiler's 'pump' terminals, so that the boiler controls the pump and keeps it running to get rid of the residual heat. It seems possible that it may just have been wired in parallel with the boiler's switched live - as per the conventional Y-Plan wiring - which is incorrect for any boiler which needs pump over-run.
Ten seconds is long enough to overheat if the pump's not running!
Incidentally, it's dangerous to turn up the tank stat - you'll get scaldingly hot water coming out of the hot taps! Far better to turn the boiler stat *down*, and see whether that cures the problem. But *do* check the pump wiring, and that the boiler's pump control is working properly if the wiring is correct.
Reply to
Roger Mills
I really appreciate your help and advice Roger!
The person/s who fitted the CH at new-build (15+ years ago) did not leave any identification on the three cables (which emerge from under the floorboards) near to the cylinder, pump and 3 way valve, and used assorted chocolate blocks rather than the approved connection box. I am not sure yet whether they routed the room thermostat wiring back towards the cylinder area, or routed them back to the boiler etc etc. If it were summer I would simply disconnect everything, and then using a multimeter and long piece of flying wire trace which cable comes from where and then reconnect all in a manner which would be easier for me to diagnose, but in mid winter the ladies in our household prefer warmth to a totally 100% functioning heating system. So that may have to wait, although if there is time for a brief power shutdown I might study the wiring diagrams for the Y system and relate this to the rat's nest they left behind.
Well - I have more information today.
1. Last night's test - With the boiler stat set to lower than the cylinder stat the system has run perfectly overnight, and the programmable room thermostat worked correctly coping with the different night to day heating requirements (as usual).
2. This morning's test for overheating - With all TRVs wide open (in addition to the two wide-open lockshields) exactly the same symptoms occur 'sole HW' OK, 'sole CH' OK, combined 'HW & CH' OK, but boiler drops to F1 when (with CH on) the cylinder stat is switches off.
3. Your suggested pdf manual is superb, but in order to check the 10 previous fail codes I need to press and hold the MODE button, but there is no MODE button on the outer casing of my boiler. This may be because my main boiler programmer is not integrated with the boiler as in the manual. Once again the need to keep the family warm prevents me taking off the cover to see if there is a mode button near the pcb. (don't worry I strongly believe in leaving anything to do with gas to the professionals).
4. Due to the rat's nest of cables I took digital photos of all wiring before doing any disconnects and component replacements, and also only worked on only one wire being disconnected at one time. I am therefore sure that all wiring is as was at first-build.
5 . >Incidentally, it's dangerous to turn up the tank stat - you'll get
boilerstat *down*, and see whether that cures the problem.
Excellent advice - Thanks!
6. >It's worrying if the pump stops dead.
A good prompt - so tonight I did numerous manual HW thermostat on and off switch cycles with CH demand being continuous (and 120+ sec pauses in between to allow the circuit to settle). Almost all of these offs resulted in an **almost** certain pump stop followed a few secs later by an attempt by the boiler to fire (probably to feed the CH demand) and then an F1. On one occasion I **think** that the pump did not stop and everything continued with no F1. STRANGE, but this inconsistency is worrying or possibly informative. I need to check if the inconsistency depends on whether the boiler is 'alight and burning' at the time of my manual switch off of the cylinder stat.
7. Well I replaced the new 3 port valve with yet another new one ( I carry a spare for emergency) - in case the problem was microswitch related, but the same symptoms persisted so I switched back.
8. I remembered that the old cylinder thermostat seemed to have a very large lag between on and off - probably 90 degrees anticlockwise after rotating to on to get it to off again. I realise that there has to be some hysterisis or the stat would go into almost constant cycling, but to me this seems excessive, and does not match with results from the new cylinder stat.
I am beginning to wonder if this hysterisis (which I can also identify with a continuity test on my meter) hid a fault in my system. Was the cylinder stat maybe never or very rarely switching off?
a. In the summer with HW demand only, the water temp may have been governed by the boiler stat, which I would have set fairly low anyway, and possibly below the actual switch point of the cylinder stat.
b. As the weather got cooler I then required HW and CH, but once again if the cylinder stat never switched off I would not get any F1s, except on the odd occasion when the heating was left on overnight and had the lower CH demand (due to the closed thermostat radiator valves) and therefore the temp got high enough for the cylinder stat to genuinely switch off, with a corresponding F1. This could explain the unpredictability of the F1s.
c. Obviously with the burst of cold weather (and a fairly large house) I turned up the boiler thermostat and also left things running (at a slightly lower CH temperature requirement) each night. This increase in boiler temp and the restriction of the thermostatic rad valves and the slightly lower CH temp requirement may have made the old cylinder stat exceed the cut off point, resulting in unpredictable but more frequent F1s in the mornings.
d. The new cylinder stat with a much smaller lag (hysterisis) would obviously be more likely to switch off and on, and thus increase the F1 frequency even more.
Thanks Dave M
Reply to
90 degrees is too much. Something like 30 degrees which is about +/- 5C from the nominal setting.
with a (mid posn.) 3 port valve the demand signal to the boiler is continuous in HW and CH+HW modes. There is a delay in the demand signal to the boiler when going to CH only mode. Usually about 10 seconds (but depends on how stiff the valve is).
I've looked in the manual and F1 is an ignition lockout. It's possible that when the ignition is becoming marginal it works when cold but maybe fails occasionally when hot. F4 is the more serious flame failure during burning. All the fault codes are listed on page 38.
It might be possible to catch the boiler misbehaving.
Reply to
Ed Sirett
Thanks for your input Ed!
Yes I thought it probably was, and I wonder if it has not been switching off, and therefore hid the F1 problem for some time. The new stat is identical in make and design except is more like 30 degrees.
When you say there is a delay in the demand signal, I **think** I detect this length of delay when moving from HW+CH to CH only, and it is after this delay that the F1 sometimes displays. Should the pump be stopping during this period?
Yes - I saw in the manual that F1 is ignition lockout, and this makes sense, but I cannot understand why it happens. Just to focus my thoughts - The fault appears to occur in this sequence and I have replicated the fault and the non fault tonight several times but have no control over which result occurs.
1. I have HW and CH demand 2. The HW demand is fulfilled (or I turn down the cylinder stat) 3. The pump stops very briefly, the three port valve moved to CH only and then one of the following occurs
EITHER a. The pump stop is 1 sec max and then it refires and all is all OK with no F1 or b. The pump stop is slightly longer and then it does not refire and the boiler F1s.
In both cases the valve moves to CH only as expected. This is a new valve head, and I even replaced this with yet another new one in case the microswitches were faulty.
I checked with my son tonight and I was mistaken that it was an F4 - it was in fact an F5 - overheat fault. This occured only once under unknown conditions and is not my major concern at this point. Sorry for the misinformation to you and Roger!
At no point have I replaced the entire valve assembly. IF the ball was distorted (towards the CH port), could this sometimes restrict the travel in the head and therefore stop the correct microswitch actions. AND does one of these microswitches have responsibility for the pump and boiler refire?
I shall be busy for a few days, but I could presumably park the valve in CH and HW mode, diconnect the header and then rewire the other new header attached to a new valve in open air to see if the F1 recurrs with the new mechanical section of the valve.
Dave M
Reply to
In an earlier contribution to this discussion,
The more I read of your experiments, the more convinced I am that it's an over-heating problem because the pump isn't being controlled properly.
You may need to refer to the Y-Plan wiring diagram at
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and to the explanation of how the 3-port valve works at
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system should be different from the Y-Plan system shown, in the following ways: * The boiler should have a permanent live feed from (1) in addition to the switched live from (8) * The pump should be connected to the boiler's 'pump' terminals, not to (2), (3) and (8)]
When there is a demand for HW and CH at the same time the valve will be at its mid position, and the boiler will receive a demand from (1) on the cylinder stat. When the HW demand is satisfied and the cylstat switches to (2), the boiler demand disappears temporarily (for a few seconds). With the grey wire to the valve now live, the valve starts to motor towards to CH-only position and when it gets part-way there a micro-switch is triggered which makes the orange wire live, re-asserting the boiler demand. It is essential that the pump continues to run while the valve moves - otherwise the residual heat in the boiler's heat exchanger will cause it to overheat even though it isn't firing. I suspect that the pump *isn't* continuing to run for one of the following reasons: * Pump live is connected to (8) instead of the boiler's pump connection, causing the pump to stop when the boiler demand is switched off * There is no permanent live connection to the boiler, only a switched live * There is a fault in the boiler's pump control circuit
If you want to check out my theory, temporarily wire the pump into a 13A plug and run it constantly, and see whether you *
still* get the F1 when you switch off the cylstat. If I'm right, you won't.
Reply to
Roger Mills
I concur. I think that you have suggested a very useful test for the issue.
I hope it works for the OP and helps resolve the issue!
Reply to
Hi and THANKS to you all!
This morning's tests were as follows:
1. Disconnect mains wiring to pump and feed with flying cable from 13A socket. a. Obviously the pump ran continuously. b. 'HW only' OK, 'CH only', 'both CH+HW' OK, AND manually switching off the cylinder stat and on again did not produce an F1. The above could be repeated numerous times.
2. I **very** momentarily unplugged the 13A flying lead and the boiler kettled immediately. I do not get this kettling when the system develops the F1 fault, but this may not overrule the overheating theory.
3. When I do switch off the cylinder stat (with all connections as normal) the pump stops, there is no kettling and definitely a few seconds delay before the F1 results. Does this maybe happen as the CH circuit attempts to refire the pump? Just occasionally the pump does not stop and then no F1 results.
4. I then reinstated the system control wiring to the pump and then in an attempt to answer my previous question - QUOTE If the ball was distorted (towards the CH port), could this sometimes restrict the travel in the head and therefore stop the correct microswitch actions. AND does one of these microswitches have responsibility for the pump and boiler refire? ENDQUOTE I removed the new valve head, manually set the old (in water circuit) 3 port base to deliver CH and HW, and then wired the new valve head to a new 3 port base (without it being connected in the water system). I then did the normal checks, and sadly the F1s continued. I guess this rules out my distorted ball theory.
4. When others are out, I will check the voltages etc as suggested by Roger.
Thanks for your assistance everyone!
Dave M
Reply to
In an earlier contribution to this discussion,
It's as I suspected. The pump stops for the few seconds the valve takes to motor far enough for mirco-switch 2 to close [1](at which point the boiler and pump demands are turned on again) - and the boiler overheats in this period and fails to restart when the demand is turned on again. If you artificially make the pump run all the time, it doesn't happen.
So you need to work out *why* the pump is stopping, and address that issue.
Having disconnected and re-connected the pump wiring, you presumably now know how it is connected. Is it connected to the pump terminals on the boiler, or somewhere else? If the latter, where?
Is there a connection to the boiler which is permanently live, in addition to the demand which gets turned on and off by the stats/valve?
ISTR that in the installer setup menu described in the manual, there is a parameter for pump over-run time. What is that set to?
[1] This also happens when the valve actuator is replaced by one which is not physically connected to the 'wet' part of the valve, so the time delay is a function of the actuator itself, rather than the valve being partially seized, which was something I did wonder about.
Let me know how you get on investigating pump over-run. I haven't run out of ideas yet, but we'll take it a step at a time.
Reply to
Roger Mills
In an earlier contribution to this discussion,
Yes indeed! I can't explain that, but am pretty sure it's lying! The OP did indicate that he had seen the occasional F5.
Seemingly it *consistently* fails to restart after the flame and pump are cut simultaneously, but is ok if only the flame is cut and the pump carries on. Sounds to me like a classic case of triggering the overheat trip. Can you conceive of a scenario where you would get a *genuine* F1 under these circumstances? [Maybe an occasional one if the ignition is marginal, but sure not *consistently* - and only with the pump stopped?]
Reply to
Roger Mills
you presumably now
Unfortunately the pump is upstairs and the boiler downstairs. When doing the permanent 240v mains (from socket) test I just disconnected the wiring to the pump at 'point of pump entry' (not at the boiler end) so working out whether the pump wiring goes to the pump terminals on the boiler will involve a long flying lead, which I need to acquire. I also need some assistance from the family, who are not available to help today.
With simulateneously 1. the boiler electrically live but not actually burning as it is at the desired temp, and 2. the cylinder stat off, and 3. the room stat off I cannot find any wires in the upstairs (location of cylinder, pump, 3 port valve and cyl stat) rat's nest ANY cable which is live.
The manual which you recommended requires me to press a MODE switch on the boiler's front panel to enter the full diagnostics section, and my boiler does not have a MODE switch. It only has 'power' and 'boiler temp' control knobs and a two digit LED display. These buttons do not have any additional facility (such as press and hold) to access the diagnostics menu and my own boiler (abbreviated) manual does not explain how to enter this diagnostic mode. So I cannot get anywhwere near the pump over-run time or a detailed failure mode history. I have Googled for other manuals, but so far without an explanation of how to enter diagnostics.
IN SUMMARY TO DATE (but correct me if I am wrong)
Symptoms: HW only mode - no probs CH only mode - no probs HW and CH mode - no probs unless the cyl stat switches off - the 3 port valve motors correctly - the pump stops - and at some stage within a few secs the F1 (failure to light) mode results. On extremely rare and unpredictable occasions the pump does not appear to stop, and then there is no F1. This might be when the boiler stat is either on or off, but I have not been able to test this yet.
1. I think this problem **may** have existed for a considerable period of time, but has maybe been masked by the old cylstat only switching off rarely, due to the very large hysterisis between 'demand heat' and 'sufficient heat' modes within the cylstat. The new cylstat has less hysterisis and therefore possibly highlights the problem of an F1 more frequently. Higher settings of the boiler temp during the winter might also explain an increase in the F1s (as the boiler temp more frequently exceeds the cylstat setting).
2. The three port valve always positions itself correctly for: HW only mode - no probs CH only mode - no probs HW and CH mode - no probs
3. Electrical faults within the dry head of the valve have been ruled out by swapping in and out a total of 3 heads (2 of which were brand new).
4. Mechanical stickiness of the wet 'shaft' part of the valve has been ruled out by connecting assorted dry heads to brand new wet sections (whilst not in the water circuitry).
5. The possibility of a distorted ball preventing the microswitches from switching during the transfer from HW+CH to CH only was also ruled out by connecting assorted dry heads to brand new wet sections (whilst not in the water circuitry).
7. If the pump is disconnected electrically from the control system and then powered via a 'flying lead' 240v socket supply, the pump continues running throughout and system does not fail to F1 on CH+HW to CH only transfer.
8. Unplugging the supply in 7 for a second causes immediate and very noticeable boiler kettling. I do not hear any kettling during an automated 'CH+HW' to CH transfer. This 'might' work against the overheating theory, but who knows?
9. I have studied the complex explanation of how the electrical parts of the 3 port valve create the actual shaft rotations, and have a vague understanding of how the spring, AC and DC cause shaft rotations. I have however tested the microswitches in the dry electrical head and can confirm that they themselves are not defective.
Next move probably/possibly has to involve me identifying where the wires within the three mains cables which enter the upstairs ''cylinder, pump, valve area' connecte to the downstairs boile and programmer (and also to the roomstat).
I will then be in a position to answer Roger's questions about electrical connections between all components. I doubt that I will be able to do this in the near future as the family have been very tolerant with my investigations to date, and it is only fair to spend more time with them for a few days.
I shall however continue to read any posts you (all) kindly offer. I know that the problem and hopefully the ultimate solution require much more than one word answers, and therefore appreciate your input even more.
I wish you all a happy and healthy festive season!
Cheers! Dave M
Reply to
In an earlier contribution to this discussion,
I suspect that you unplugged the pump while the burner was firing, whereas it isn't firing during the mid-position to CH-only transition, which may explain the difference.
Reply to
Roger Mills
You are correct. Incidentally I have only ever had one F5, and this was reset by my installer who could not offer an explanation as to its cause. This was before I discovered the current problem.
Like you - I think that the F1 may be misleading. and is simply the control system telling me that it has not ignited due to some defect in the control system or boiler other than a genuine fail to ignite fault.
Thanks Dave M
Reply to
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> if you don't have one) you may get several errors at the same time, and can
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> if you don't have one) you may get several errors at the same time, and can
Hi - reading the above.......
I get F1 errors from time to time but mine are specific to weather.
The flue is situated close to a corner between 2 walls (but not inside installation dimensions). When the wind blows exceptionally hard (F7 and above) the boiler fails with the F1 error.
I am sure this is because the pressure into the flue overcomes the pressure that the boilers fan create. This would mean if the boiler were to light that exhaust gasses would not be able to escape.
So in my case the boiler is failing safe. Fortunately this does not happen often.
PS the instruction manual says that to reset the boiler you press the re-set button beneath the display (with a small nail)
Works every time for me.
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