Another heating problem question!

I added TRVs this weekend and the week before replaced the boiler thermostat. Since doing this I've noticed that the downstairs is not as hot as it used to be - even with the TRV heads off. I've also noticed a lot of boiler cycling (old Baxi WM 531 RS boiler).
Previously the living room (large room with 2 radiators) used to get quite hot with the heating on - now it gets warm, but not warm enough really. I've tried rebalancing (which previously got the downstairs nice and toasty) but that doesn't appear to make a significant difference. I did struggle to get much of a temperature drop on some radiators - some only had as little as a 3 degree drop with just a 1/8's of a turn on with the lockshield. The highest drop appeared to be on the largest (and furthest radiator which isn't getting quite as hot) which was 20. The majority of the rest were about 5-8 degree drop.
The pump (UPS 15-50) is running on its slowest speed and always has done. Anything more than this and there's a noticeable noise from the pump/pipework. I did a test last night and increasing the pump speed altered the boiler cycling times only slightly (5 seconds different) and failed to make any difference to the temperature of the pipes to the largest downstairs radiator.
Specifically, with the boiler thermostat set to 3 (with 5 being highest) the boiler would heat the water for
Boiler thermostat setting Pump setting Time boiler on Time boiler off Pipe therm 1 Pipe therm 2 3 1 1 min 35 secs 1 min 45 secs 50 30 5 1 2 min 25 secs 1 min 20 secs 50 30 3 3 1 min 40 secs 1 min 45 secs 50 30
The pipe thermometer readings were from the large (9') radiator which was the one which got cold when it wasn't balanced properly.
As you can see, the boiler is cycling about every 2 minutes and changing the pump speed made little difference.
The radiators closest to the boiler do get hot and the downstairs radiators don't get as hot, but are hot.
I've got a thermometer (built into a small travel clock) and I've yet to make the temperature in the living room more than 20.5 even though I've set the wall stat in the hall to anything up to 25. Note, I did these checks with the TRV heads off - so they're not restricting the flow and I got the same reading with both TRV's set to 5 (the highest on the Pegler Terrier II).
I'm sure the cycling times dropped when I changed the boiler thermostat, but I'm confused that increasing the pump speed makes little difference.
What sort of noise would you expect from my pump on speed 3? The pump is very quiet on speed 1 but becomes quite noisy on speed 3 (and its about 3" away from a bed in a spare room - so I don't want to it be too noisy). I've checked that the system has been bled properly including the pump.
I'm going to continue tweaking the balancing of the radiators - but I'm puzzled that it used to get uncomfortably hot but now it doesn't even when the TRV's are off and that the pump speed makes little difference to the temperature and boiler cycling.
Any ideas?
Thanks
David
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Don't know what kind of TRVs you've got, but on my old house if we wanted a radiator to get super-hot, we had to unscrew the top unit of the TRV a few turns. Even though they were fully opened, it seemed that the valve was partially closed and only the unscrewing made them fully open.
Tony

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On Thu, 11 Dec 2003 18:43:55 +0000, Tony wrote:

It is likely that the old failing thermostat was effective set quite a high output temperture to the boiler.
Is it possible that the water heating coil is taking all the flow away from the heating circuit - is there any control on this?
Seems to me that there must be quite an easy path for the water to avoid going to the big rad.
I wonder if turning off all the rads except the big one one would make any difference? i.e. all the heating is going through the coil and/or bypass pipework.
HTH
-- Ed Sirett - Property maintainer and registered gas fitter. The FAQ for uk.diy is at www.diyfaq.org.uk Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
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The water heating is separaetely controlled and wasn't turned on during the measurements.
I did twiddle a lockshield in the hall today (turned it from 1/2 turn to 1/4 turn I think) and this evening the living room felt quite a bit warmer and the room temp appeared to reach 21.4!!! I'm thinking its probably just a balancing thing.
Incidentally, I'm sure I can hear a bubbling noise from the boiler towards the end of its heating period - and that's with a thermostat setting of 3. I've turned it down to 2 now to see what happens to the room temp. It most certainly does seem that this thermostat is working differently to the old one. The old thermostat was marked 106 oC and this new one is marked 90oC - but as people said before, 106oC is above boiling point, so it may not be a reliable figure.
Anyway - thanks - I think I'll just try a little more twiddling (including turning off all the other rads and seeing what happens).
Thanks
D
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Some TRVs have a built in pre-set sort of lockshield valve - the Drayton ones I've just fitted have and you require a special tool to adjust it. And they appear to come set back slightly and as I don't yet have the tool so just opened up the other lockshield valves to compensate. Perhaps if you're running at a very slow flow rate this factory setting is too low?
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On Thu, 11 Dec 2003 18:37:04 -0000, "David Hearn"

Boiler short-cycling means that the heat the boiler generates is not being taken away fast enough by the circulating water. Symptoms are that the boiler fires continuously at first, i.e. when the system is cold, but as the system warms up to temperature the boiler shuts down for a short while every few minutes.
The fundamental causes of short-cycling are:
1) Inadequate pumping, i.e. pump set to too low a speed, or it is damaged.
2) Restricted flow to the heating circuit caused by (a) partially closed radiator valves, (b) sludge or other obstruction in pipe work, or (c) pipe bore too narrow.
3) Excessive by-pass flow.
In the case of 1) and 2), the return pipe temperature at the boiler fails to reach full temperature or even remains quite cool, and some or all of the radiators will have cool return connections. The return temperature should reach within 11C of the flow.
In the case of 3), the by-pass circuit is returning too much hot flow water back to the return, and the return at the boiler may be almost as hot as the flow. However, the return water from the radiators, before it joins the by-pass return, will be too cool.

What procedure did you use to re-balance? Are you starting with all LSVs wide open, and turning DOWN the LSVs on the HOT rads according to http://www.diyfaq.org.uk/plumbing/rad-balance.html , rather than just trying to open up the cool ones?

[Reformatted for clarity]
Boiler    Pump    boiler    boiler    Pipe    Pipe stat        on    off    1    2 3    1    1m35s    1m45s    50    30 5    1    2m25s    1m20s    50    30 3    3    1m40s    1m45s    50    30

50C on the flow is not enough. What is the temperature at the boiler flow on number 5? It should be over 80C. It seems you have hardly any flow to this rad so you need to fully open its LSV and close down some of the hotter ones.

Then the system is not balanced. They should all get equally hot (or cool!!) even if the boiler is short cycling. I suggest you study the above balancing FAQ and try again. Note that all the flow ends should be at virtually the same temperature, and within a few degrees of the boiler flow temp.

Is that what you are using to measure the flow and return temperatures? If so, the results are probably miles out!!

If the system is unbalanced to the extent that the radiator is not getting hot, the room will not warm up much above ambient anyway.

It seems to me that (1) in changing the boiler stat you have now got the boiler set at too low a temperature. It should be set at up to 82C flow temperature, and (2) you must have closed the LSVs to install the TRVs. Therefore you need to re-balance them. Did you record their original settings?
In addition, Ed's points about the by-pass and the cylinder coil need checking out. If you have no motorized valve or TRV on the cylinder coil, it must be balanced with a series gate valve used as a LSV, just as if it was a radiator. You can get 'locking' gate valves for this purpose.
Since the system was working previously, sludge and inadequate pipe size can probably be ruled out.
-- Phil Addison The uk.d-i-y FAQ is at http://www.diyfaq.org.uk / Remove NOSPAM from address to reply
-- Phil Addison The uk.d-i-y FAQ is at http://www.diyfaq.org.uk / Remove NOSPAM from address to reply
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wrote:

No 3 might be something - I've covered that below though.

Well, my procedure was to open up all the lockshields and then turn the lockshields on the rads closest the boiler (the hottest ones) to get them as closed as possible yet still giving an adequate temperature drop and still hot to the touch. It wasn't a 'to the letter' following of the FAQ.

I've yet to manage to get the thermometer onto the boiler pipes directly (very tight squeze above the boiler or floorboards up directly above the boiler). I'll try to get this done tonight and see what's actually coming out of it.

I'm pretty sure that most of the radiator flow ends aren't at the same temperature - I'll work on that part by rebalancing (and following the FAQ more accurately I guess).

No, I've got 2 pipe thermometers for the radiator feeds - I'm just using that thermometer as a basic indication of room temp.

I'll check that tonight hopefully.

I recorded their original settings, but I replaced the lockshields, and I've no idea whether the number of turns are transferrable. Initially I set them to be what they had been on the old ones, but I soon noticed it wasn't balanced properly - hence doing a (basic) balancing.

The system has 2 motorized valves - one for heating and one for hot water. When I balanced it, I did so with the water off. The water is only heated for an hour or two morning and evening and wasn't being done when I did the room temperature check.
I did notice a small 15mm pipe with a gate valve on it which appears to bypass the motorized valves. After being unhappy with the balancing I did twiddle it a little and returned it to the same place it was set to before. Should this be open or closed - or just adjusted? I assume its a safeguard so that when both valves are shut and the pump/boiler is on, that there is some flow back to the boiler? If that is the case, I guess it must be open, but not enough to cause too easy a path back to the boiler.

Whilst I didn't use any sludge remover before installing TRVs, I did remove each radiator and flush it through thoroughly, so any sludge etc would only be that in the pipework (or distubed at the bottom of the header tank when it refilled).
Thanks for the very helpful hints - I'll report back with the temperature of the boiler output and I'll give the balancing a better go. I wasn't aware before that the output pipe of the radiators should all be roughly the same.
Thanks
David
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In an earlier contribution to this discussion,

All the radiators are (should be!) connected in parallel - so that the input temperature is almost the same as the boiler output temperature. If there is an appreciable difference, it indicates that you are losing a lot of heat from the supply pipe - either because the flow is too low or because the pipe is unlagged and passes through a very cold space, such as under a suspended ground floor.
With all the radiator input temperatures being the same - and with the same drop across all radiators in a balanced system - it follows that all the ouptut temperatures should be the same.
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Don't forget to add inhibitor to the CH water.

Yes, a radiator is designed to give out its rated heat when it has a certain specified temperature drop from flow to return, typically 11C. Getting them all the same is the whole point of balancing.
-- Phil Addison The uk.d-i-y FAQ is at http://www.diyfaq.org.uk / Remove NOSPAM from address to reply
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In an earlier contribution to this discussion,
I . . have just ordered an infra-red

use it yet 'cos it's a Christmas present)!

Not easy to achieve with most programmers which use the same on/off periods for CH and HW. The only way I can think of to do it is to use the main programmer for HW, setting CH to constant and actually controlling the CH at different times with a programmable room stat. Is this the accepted way?
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