boiler doesn't respond to room thermostat

Hi all,
our boiler doesn't always seem to respond to the room thermostat although the heating does come on sometimes and sometimes, but not always, the boiler does respond to turning the thermostat dial.
the hot water tank has it's own thermostat and the boiler responds to this as expected.
I've tried replacing the room thermostat but this has made no difference.
any suggestions for things to try or possible causes?
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In an earlier contribution to this discussion,

You need to provide a bit more information about your control system. You appear to have a fully pumped system with independent control (if it worked!) over the CH and DHW. This is likely to be either a Y-plan system (with a single 3-port mid-position valve) or an S-plan system (with a separate 2-port zone valve on each circuit). Have a close look at your plumbing and also at http://content.honeywell.com/uk/homes/systems.htm and tell us which you've got.
Has it always been like this - or had it used to work properly? Do the radiators get hot when the DHW is being heated, but go cold once the DHW gets hot - even if the room stat is still calling for heat?
We can give a better answer once you have answered the above questions, but my initial guess is that you've got a Y-plan system which is either incorrectly wired or has a faulty actuator on its 3-port valve.
--
Cheers,
Set Square
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O.K - It looks like it's a y-plan system with a duoval 3-way valve. The duoval was replaced last year after several yrs of use as it was sticking.

the system has been working fine for ages and ages, it's just fairly recently and intermittently started playing up. the rads don't get hot when the DHW is beng heated which might imply that the new duoval has failed I suppose.
I have a question though. Assuming the DHW is at it's set temperature, would I expect the boiler to respond to a RFH from the room stat' even if the 3-way valve was stuck or does the system "know" that the valve isn't in the correct position to deliver heat to the rads and will therefore not respond?
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In an earlier contribution to this discussion,

It "knows" in as much that - for the CH-only requirement - the boiler and pump are switched on by a micro-switch in the 3-port valve actuator, which only "makes" once the valve has moved to the correct position.
Is your actuator easily removeable from the valve? [Many come off with a couple of screws - with no danger of water leakage, because the valve itself is sealed]
If so, does the valve spindle rotate fairly easily with the actuator removed? [You should be able to turn it with your finger and thumb or, at worst, using light pressure with a pair of pliers.] If it is very stiff, that is probably the problem. If it is free, the actuator may be duff. See whether the actuator itself (when removed from the valve but still connected electrically) motors to the correct position and turns on the boiler and pump. If it doesn't, you have one or more faulty components (motor, microswitch, diode etc.) in the actuator. Whilst these can be replaced individually, it's a bit fiddly - and often easier to replace the whole actuator for 30 quid or so.
--
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Set Square
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cheers mate! :-)
removed the actuator and the valve spindle rotates really easily and the actuator doesn't do anything when switched so is therefore duff.
I'm a bit narked really as it was replaced at the end of March last year at a cost of 65 so I'm not very impressed with a 13 month life span considering the previous one lasted at least 5 years. Have now emailed Sunvic who made it to see what they say.
thanks for the help\advice.
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another question.....
I've had a response from Sunvic who said I should get 10yrs out of my actuator and that it was EXTREMELEY UNLIKELY that it had failed after a MERE 13 months! and suggested that I obtain a multimeter and test the relay.
As it happens I'm not a sparky and wouldn't know how to use a multimeter if my life depended on it.
However, if I unplug the relay from it's socket whilst the DHW is being heated the boiler switches off. When I push it back in again the boiler fires up and resumes heating water. Is this confirmation that the relay is O.K or could it still be the cause of my problem?
thanks again for help.
Steve.
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In an earlier contribution to this discussion,

Sorry, I'm not clear what this "relay" is. I'm not familiar with Sunvic products - but most other makes have direct connections - albeit via a junction box - between the 3-port valve actuator and the programmer, boiler, pump, and room/cylinder thermostats.
Are you saying that your system has a relay - as in a switch operated by an electro-magnet?
I notice that on the Sunvic website, they refer to a "Relay Wiring Centre" - which I take to be just a junction box. Is this what you're talking about?
Please remind us of the exact model numbers of the Sunvic kit you've got so that we can find the correct installation details on their website.
--
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Set Square
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On Fri, 14 May 2004 20:42:39 +0100, Set Square wrote:

My old flat had a "flowshare" system, part of that was a box with a relay in it that the 5(?, might have been 6) core cable from the 3 port valve connected to. This relay box had a base about 4" x 3" and was about 3" high.
--
Cheers snipped-for-privacy@howhill.com
Dave. pam is missing e-mail
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Without a part number, we're going nowhere
--
geoff

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sort of expected you guys to instantly know - you all being d.i.y gurus... :lol
in the cupboard with the pump and activator are 2 boxes on the wall. one is a simple wiring junction box. The other box contains the relay.
The sunvic website below has the relevant images and numbers....
http://www.sunvic.co.uk/ps.htm
Top right is the relay 2272 - 337
Middle left is the Duoflow Relay wiring centre - RJ 2802
hastily chucked together web-page with better detail of my boxes and wiring diag' at > http://www.gooduse.com/other/heating.htm
so... when I pull the relay from it's socket the boiler stops heating water. plug it back in and boiler fires up again.
I assume that actuator sends signal to relay saying dhw or heating or both and relay switches accordingly. I also assume that the boiler can't respond to RFH from room stat unless actuator can rotate accordingly, send a signal to relay which then tells the boiler to fire up.
Is my understanding correct and can I still assume that the actuator is knackered as it doesn't motor around or could the relay be stuck?
thanks....
Steve
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... But not mind readers
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geoff

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In an earlier contribution to this discussion,

Also, those of us who (unlike Geoff) are pure DIY-ers will have direct experience of only a limited number of makes and models - depending on how many houses we've owned. We can often extrapolate that knowledge and experience to work out what's going on with similar but different equipment - provided we have access to the appropriate information.
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Set Square
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apparently this is a direct link to the relevant wiring diagram....
http://www.sunvic.co.uk/rjtypicalprog.pdf
which is much better than the crap image I posted!
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In an earlier contribution to this discussion,

Yes, I had found it myself in the meantime, and it makes things a lot clearer.
The fact that the hot water works with the relay plugged in but not with it out in does *not* necessarily mean that the relay is ok!
In its un-energised state, the relay has contacts which switch the boiler and pump on in the hot-water-only situation. Pull the relay, and the boiler will goe off!
When heating is selected at the programmer, and the room stat is calling for heat, the relay is supposed to switch to its energised position - which provides an alternative supply to the boiler and does things to the actuator. Perhaps it isn't switching when it should.
You could check this by: * Making sure that CH is on at the programmer * Getting an assistant to adjust the room stat so that it clicks on and off * See what happens to the relay. If ok, you should hear it click on and off in synch with the room stat. [If you put your thumb on it, you should *feel* it]
If the relay *doesn't* go on and off, it could be due to: * Duff relay * Duff programmer and/or room stat * Duff wiring between programmer, room stat and relay
HTH.
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Set Square
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tried all that. I can see both sets of contacts that the relay switches between and nothing happens. the thermostat has been replaced as I assumed it was that that had failed in the first place.
it seems unlikely that the wiring has suddenly devoloped a fault so I'm going to replace the relay I think. It's currently the number 1 candidate and a new one is only a few .
let you know.
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Aha, 5601 actuator head
it's not a spring return, it keeps driving round until it reaches the desired position (depending on which of the three wires is live) and then is switched off by a microswitch inside.
With the relay unplugged, there is no drive to positions - you can't expect anything to work
I'll have a look tomorrow
--
geoff

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