Central heating thermostat

[Alan Stirrup]

Hi all, my condenser boiler central heating has started to do strange things so I set about trying to diagnose the problem. When I got to the thermostat I found that there was no power to it, could anybody tell me where this is powered from please? It is an old system, almost 30 years old so in reality it could do with being replaced but I can hardly afford to switch it on let alone replace it!

 

[freddo]

The power to the thermostat is likely only to be present if the time clock for the heating is set to on.

 

[davesparks]

When I got to the thermostat I found that there was no power to it, could anybody tell me where this is powered from please?

You need to give us some details for us to be able to help with this.
What controls do you have for the system? Is it a combi boiler or a conventional system with motorised valves etc?
Do you have a seperate programmer/timeswitch and thermostats or something else?

Also what are you using to test for voltage? And what points did you test between?

In a conventional heating control circuit the room stat is wired in series with the CH channel of the programmer. So the room stat receives power only when the programmer CH channel is on.

 

[Alan Stirrup]

The power to the thermostat is likely only to be present if the time clock for the heating is set to on.

Thanks for the reply Freddo, I tried it with the CH both on and off, this was the reason I posted as I can't figure out what else it could be?

 

[buzzlightyear]

Thanks for the reply Freddo, I tried it with the CH both on and off, this was the reason I posted as I can't figure out what else it could be

post some pics up of the set up .

 

[buzzlightyear]

I tried it with the CH both on and off

either the time clock or the wall thermostat .

 

[Alan Stirrup]

You need to give us some details for us to be able to help with this.
What controls do you have for the system? Is it a combi boiler or a conventional system with motorised valves etc?
Do you have a seperate programmer/timeswitch and thermostats or something else?

Also what are you using to test for voltage? And what points did you test between?

In a conventional heating control circuit the room stat is wired in series with the CH channel of the programmer. So the room stat receives power only when the programmer CH channel is on.

Hi Dave, separate timer/thermo, conventional Baxi boiler. I’ve tried to attach pics of the thermostat but each pic was too large even with adjustments. The thermostat appear to be called T.R.A.C if that makes any sense?

 

[Alan Stirrup]

Hi Dave, separate timer/thermo, conventional Baxi boiler. I’ve tried to attach pics of the thermostat but each pic was too large even with adjustments. The thermostat appear to be called T.R.A.C if that makes any sense?

Also, if it helps, the pump seems to run continuously even when the CH has been off for hours.

 

[brianmoooore]

Faulty pump over run control?

 

[freddo]

Zone valve stuck open? open

 

[Lucien Nunes]

We really need pics of the wiring both at the thermostat and preferably at the wiring centre. Perhaps you could switch the resolution of the camera down to a lower setting and retake them?

 

[Alan Stirrup]

Hi all, I managed to resize the images, let me know if you need any more.

 

[timhoward]

I’m suspicious that the connection on the right in the photo above is not a good connection.

But in general you need to follow it through one stage at a time.
Time clock. Wall stat. Zone valve (3 port) or zone valves (2 x 2 port). Pump. Boiler

There should be a junction box, usually in the airing cupboard where all of this comes together and 5-10 minutes with a 2 pole tester is normally enough to work out what is going wrong.
A photo of this box is rather important to being able to help more.

 

[Lucien Nunes]

I’m suspicious that the connection on the right in the photo above is not a good connection

Yes it looks like the screw is clamped onto the insulation. In practice there is usually continuity but it should be corrected.

The OP mentioned the boiler doing 'strange things'.... what exactly is the fault that led to investigating the room stat?

 

[Alan Stirrup]

Thanks guys, I'll try and upload a pic of the junction box later today. That connection has been like that since the heating was installed nearly 30 years ago, the issue now is there is no power in the cables. The issue that prompted me to check the thermo was the temperature upstairs was intolerable and the pump was running continuously even when the heating had been off for several hours.

 

[Lucien Nunes]

That connection has been like that since the heating was installed nearly 30 years ago, the issue now is there is no power in the cables.

Badly made connections can eventually go open circuit, as the surfaces where the wire is just barely touching oxidise over time. If you were checking for presence of a feed by touching your meter probe on the screw, loss of continuity would cause a zero reading, as that is probably the incoming feed from the programmer. (I expect the stat output is the yellow core oversleeved in red)

We seem to have three different symptoms with no certainty of how they relate to each other.

• Room continues heating when it shouldn't
• Pump runs when it shouldn't
• No feed to room stat

Definitely need to see inside the wiring centre and, if it's not obvious from that, the configuration of motorised valves (Y-plan, S-plan etc.)

 

[timhoward]

The issue that prompted me to check the thermo was the temperature upstairs was intolerable and the pump was running continuously even when the heating had been off for several hours.

I have a feeling this could be two faults.
Pure speculation but my guess would be that (as already mentioned above) initially the zone valve head stuck open. That could lead to boiler and pump being on 24/7 with only the overheat stat on the boiler to possibly interrupt proceedings.
In turn being on perpetually could have then helped an old time clock to give up the ghost.
Complete guesswork though.

The first test is whether when you ask the time clock to call for heat, a terminal in the wiring centre becomes live.
If nothing changes in the wiring centre then the time clock itself is the first suspect.

Also, do you have one or two zone valves?
With everything off, does the little lever move freely on one of them (or the only one)?

 

[Alan Stirrup]

I have a feeling this could be two faults.
Pure speculation but my guess would be that (as already mentioned above) initially the zone valve head stuck open. That could lead to boiler and pump being on 24/7 with only the overheat stat on the boiler to possibly interrupt proceedings.
In turn being on perpetually could have then helped an old time clock to give up the ghost.
Complete guesswork though.

The first test is whether when you ask the time clock to call for heat, a terminal in the wiring centre becomes live.
If nothing changes in the wiring centre then the time clock itself is the first suspect.

Also, do you have one or two zone valves?
With everything off, does the little lever move freely on one of them (or the only one)?

I'll run a test on the time clock, Tim, hopefully this will give us a better indication of what's going on. I have one zone valve and the lever moves freely without resistance.

 

[timhoward]

I have one zone valve and the lever moves freely without resistance.

If this is the case without calling for hot water or central heating AND it’s the Honeywell style unit I’m imagining then I think you have a problem there as the lever should be quite tough to move with everything off. It should feel as though you are overcoming a strong spring. It sounds as though it’s stuck.

With power off, the cover comes off with a small screw near the lever. If you take the cover off I’d imagine you could then see if it’s sticking or not. The gear teeth may look shiny and worn.

If required, the head is a fairly easy replacement as long as you note where the wires go, part is available at Screwfix. Sadly you need the more expensive 3 port head.

(I appreciate you are not looking for extra expense but if it were my house I’d get a plumber to change it to 2 x 2 port valves. The heads are much cheaper for future replacement and 3 port valves can leave the motor running perpetually for hours on end after one permutation of actions. )

 

[Lucien Nunes]

If this is the case without calling for hot water or central heating AND it’s the Honeywell style unit I’m imagining then I think you have a problem there as the lever should be quite tough to move with everything off.

Assuimng this is a 3-port valve, (did we confirm that explictly?) this is true only if the last demand was for water, which would leave the valve idle in the spring refurn (B) position if the last demand was for heating the valve will be parked in the A position with the motor energised and the lever will be free to move. Briefly demanding hot water only, should release it back to the B position.

 

[timhoward]

Assuimng this is a 3-port valve, (did we confirm that explictly?) this is true only if the last demand was for water, which would leave the valve idle in the spring refurn (B) position if the last demand was for heating the valve will be parked in the A position with the motor energised and the lever will be free to move. Briefly demanding hot water only, should release it back to the B position.

Thank you - that brings up three things!
1 - you are right, he said he had one zone valve but we don't know for sure it's a 3 port.
2 - when I said "everything off" in my head that meant the fused spur to the boiler and associated control wiring but I should have been clearer.
3 - it's somewhat ironic that I even mentioned this behaviour of last call for heating without considering the system could still be powered....
Some photo's will hopefully add some clarity in due course.

 

[Alan Stirrup]

If this is the case without calling for hot water or central heating AND it’s the Honeywell style unit I’m imagining then I think you have a problem there as the lever should be quite tough to move with everything off. It should feel as though you are overcoming a strong spring. It sounds as though it’s stuck.

With power off, the cover comes off with a small screw near the lever. If you take the cover off I’d imagine you could then see if it’s sticking or not. The gear teeth may look shiny and worn.

If required, the head is a fairly easy replacement as long as you note where the wires go, part is available at Screwfix. Sadly you need the more expensive 3 port head.

(I appreciate you are not looking for extra expense but if it were my house I’d get a plumber to change it to 2 x 2 port valves. The heads are much cheaper for future replacement and 3 port valves can leave the motor running perpetually for hours on end after one permutation of actions. )

If this is the case without calling for hot water or central heating AND it’s the Honeywell style unit I’m imagining then I think you have a problem there as the lever should be quite tough to move with everything off. It should feel as though you are overcoming a strong spring. It sounds as though it’s stuck.

With power off, the cover comes off with a small screw near the lever. If you take the cover off I’d imagine you could then see if it’s sticking or not. The gear teeth may look shiny and worn.

If required, the head is a fairly easy replacement as long as you note where the wires go, part is available at Screwfix. Sadly you need the more expensive 3 port head.

(I appreciate you are not looking for extra expense but if it were my house I’d get a plumber to change it to 2 x 2 port valves. The heads are much cheaper for future replacement and 3 port valves can leave the motor running perpetually for hours on end after one permutation of actions. )

Thanks Tim,
I've just taken the head off and the lever is free moving (I can't see the gubbins as it's pretty well sealed,) I can see the female "D" slot that the valve goes into and I've moved it with a screwdriver which presents with substantial resistance. The unit is an American made Danfoss, which I doubt will be available these days although the motor is a Drayton Synchron. What would be a suitable like for like replacement in your opinion?

 

[timhoward]

@Alan Stirrup Danfoss heads and valves are very much still available. Does yours have 2 or 3 pipes (the 3 port version sits on a T )
While I have a strong suspicion that the zone valve is part of the problem (based on experience of what is most likely to break) we haven't done enough to confirm this, or prove that it's the only problem. (Also, if the valve itself is stiff, a new head will burn out very quickly, so it might need an entirely new valve fitting)

So before going any further you do need to do some electrical tests. Did you get anywhere regarding some photographs? (e.g. the wiring centre). You need to be sure that the controller is calling for heat, the wall stat is receiving power, and in turn energising the supply to the zone valve.

It wouldn't be expensive to get a sparks in to diagnose this by the way - I'd expect to have an understanding of what is going on in under an hour.

 

[littlespark]

OP is in Liverpool if a nearby member is up for a look.

I don't think Tel will be sober enough yet.

 

[Alan Stirrup]

Thank you - that brings up three things!
1 - you are right, he said he had one zone valve but we don't know for sure it's a 3 port.
2 - when I said "everything off" in my head that meant the fused spur to the boiler and associated control wiring but I should have been clearer.
3 - it's somewhat ironic that I even mentioned this behaviour of last call for heating without considering the system could still be powered....
Some photo's will hopefully add some clarity in due course.

@Alan Stirrup Danfoss heads and valves are very much still available. Does yours have 2 or 3 pipes (the 3 port version sits on a T )
While I have a strong suspicion that the zone valve is part of the problem (based on experience of what is most likely to break) we haven't done enough to confirm this, or prove that it's the only problem. (Also, if the valve itself is stiff, a new head will burn out very quickly, so it might need an entirely new valve fitting)

So before going any further you do need to do some electrical tests. Did you get anywhere regarding some photographs? (e.g. the wiring centre). You need to be sure that the controller is calling for heat, the wall stat is receiving power, and in turn energising the supply to the zone valve.

It wouldn't be expensive to get a sparks in to diagnose this by the way - I'd expect to have an understanding of what is going on in under an hour.

I have taken pics of the wiring centre I just have to convert them on my laptop so they'll load. Mine is the three pot sitting on the "T" I did a hand test on the valve and it moves freely with some resistance, probably just a little more than say, a gate valve. I've set it manually to heating and water and the downstairs heating has balanced out correctly so I'm of the opinion that the head unit has died mid position hence the imbalance and no signal to the thermostat. I'll try and load the pics tonight and thank you very much for your help so far, we seem to be heading in the right direction with your guidance.

 

[123]

The 3 port valve head should have no affect on the room thermostat getting voltage or not, it should go from the heating programmer to the thermostat.

 

[brianmoooore]

The 3 port valve head should have no affect on the room thermostat getting voltage or not, it should go from the heating programmer to the thermostat.

And then to the 3 port valve, so don't condemn the valve just yet.

 

[Alan Stirrup]

Here's the pic of the junction box in the airing cupboard. I've done a visual check at the back of the timer and all the wires are located.

 

[brianmoooore]

Hmmm, a surface pattress box and strip connector, rather than a purpose made heating connector box, where all the connections are labelled.
I think the yellow with the red sleeve, near the middle, is the heating wire from the room stat, so the red in the same cable is probably the feed to the room stat, and the wire joined to it on the strip will be the heating on wire from the programmer.

 

[Alan Stirrup]

Hmmm, a surface pattress box and strip connector, rather than a purpose made heating connector box, where all the connections are labelled.
I think the yellow with the red sleeve, near the middle, is the heating wire from the room stat, so the red in the same cable is probably the feed to the room stat, and the wire joined to it on the strip will be the heating on wire from the programmer.

That's the quality you got with new build houses 28 years ago, Brian and now it's coming home to roost!

 

[littlespark]

We can only guess at what all the wires are.

The fact that it’s in a pattress and not a proper joint box… we have no clue what diagram the installer was following.

 

[freddo]

We can only guess at what all the wires are.

Looking at what terminals the valve is connected to greatly reduces the number of unknowns.
Terminals from left to right: Hot water on from timer to cyl stat, Hot water off from programmer and cyl stat, Boiler call for heat, Heating on from programmer to room stat, Heating call from room stat, Neutral. The last one could be permanent live or pump overrun from boiler. The block on its own earth.

 

[timhoward]

We can only guess at what all the wires are.

But it's much more fun this way! In fact Danfoss 3 port zone valve wiring is a known entity and has stayed the same luckily even for 30+ years!
As per @freddo 's comments:
Grey is Hot Water Off
Brown/White is Heating On
Blue is Neutral
and Orange is the output signal to ask the boiler to fire up.





So with 100% certainty we can say that with the Heating set to ON and stat all the way up then 2 and 3 should measure 230v to Neutral (marked)
I agree with Brian and Freddo that 1 is the controller asking for heat. So this should also measure 230v to Neutral.
Obviously this needs doing very carefully.
That will quickly reveal what is going on.

 

[buzzlightyear]

1) when you call for heat does the boiler kick in when the time clocks on.
Does the boiler kick in when you
Turn the stat on
2) does the stat on the cylinder call for hot water
3) does the hot water comes in.
Zone valve work from the time clock
Does the valve move.
Is it a two chanel time clock.

 

[Alan Stirrup]

But it's much more fun this way! In fact Danfoss 3 port zone valve wiring is a known entity and has stayed the same luckily even for 30+ years!
As per @freddo 's comments:
Grey is Hot Water Off
Brown/White is Heating On
Blue is Neutral
and Orange is the output signal to ask the boiler to fire up.


View attachment 105004


So with 100% certainty we can say that with the Heating set to ON and stat all the way up then 2 and 3 should measure 230v to Neutral (marked)
I agree with Brian and Freddo that 1 is the controller asking for heat. So this should also measure 230v to Neutral.
Obviously this needs doing very carefully.
That will quickly reveal what is going on.

Fantastic, thanks Tim I'll check this tomorrow. Thanks Buzz I'll reply to your helpful questions tomorrow too.

 

[Alan Stirrup]

I'll test the wires later today when I get home from work but I have a quick question to ask. Would the wiring on my thermostat accommodate one of these digital/programmable units such as this?

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[buzzlightyear]

Before you start ordering some thing
That might not be compatible. With the system, for a replacement dryton stat.

 

[brianmoooore]

Would the wiring on my thermostat accommodate one of these digital/programmable units such as these

It looks like you may have the neutral present at the stat, that some installations lack, but in my experience of 'stats similar, but not identical, to the one in the link, it might need a permanent live to preserve its programming, which will need the 'stat wiring to be arranged so that is is before the programmer instead of after.
The one's I have in one of my properties will default to their 'off' position if their power is interrupted.

Edit: Also worth noting that there are two types of these kinds of 'stats. Ones with the temperature sensor built in, and ones where they connect to a remote temperature sensor on a 2m or so lead.

 

[Alan Stirrup]

It looks like you may have the neutral present at the stat, that some installations lack, but in my experience of 'stats similar, but not identical, to the one in the link, it might need a permanent live to preserve its programming, which will need the 'stat wiring to be arranged so that is is before the programmer instead of after.
The one's I have in one of my properties will default to their 'off' position if their power is interrupted.

Edit: Also worth noting that there are two types of these kinds of 'stats. Ones with the temperature sensor built in, and ones where they connect to a remote temperature sensor on a 2m or so lead.

Is that the blue wire for neutral, Brian, I don't think that's connected at the junction box.

 

[Alan Stirrup]

So 1&3 are pulling 244 & 245 volts respectively but number 2 is dead, do we have a culprit?

 

[brianmoooore]

Is the 'stat turned up?
The red at 1 should be the other end of the red at the 'stat, so check there as well.
The blue may not be connected at the moment, but it can be, if needed.

 

[Alan Stirrup]

Is the 'stat turned up?
The red at 1 should be the other end of the red at the 'stat, so check there as well.
The blue may not be connected at the moment, but it can be, if needed.

Yes Brian, the stat was turned up thanks.

 

[Alan Stirrup]

So now we have power in the stat wire, I've no idea why, all I did was open the connections on that block, push them in further and tightened them up.

 

[brianmoooore]

Does that mean everything works now?

 

[buzzlightyear]

Does that mean everything works now?

Drum roll with the elephant on top.

 

[Alan Stirrup]

Does that mean everything works now?

It seems to be, Brian, however there may be an issue with the three port valve we discussed earlier. I placed this to water and heating manually and haven't tested by flicking over to water only yet. I'm not to worried about that though as I can wait for the warmer weather and get it converted to a two port as suggested.

I think the only thing that remains is where I connect the blue neutral wire in the junction box so that I can change the thermostat?

 

[brianmoooore]

So now we have power in the stat wire, I've no idea why, all I did was open the connections on that block, push them in further and tightened them up.

The wire could have been tightened down on the insulation, instead of bare copper. It might be still on the insulation, but the screw has now cut through it.
Blue wire needs to go to neutral, which timhoward has identified in post #33.
Congratulations on a successful fault finding.

 

[Alan Stirrup]

The wire could have been tightened down on the insulation, instead of bare copper. It might be still on the insulation, but the screw has now cut through it.
Blue wire needs to go to neutral, which timhoward has identified in post #33.
Congratulations on a successful fault finding.

Thanks very much Brian and to everybody else who has contributed to helping me resolve this issue you gents are fantastic and really generous the way you give up your spare time to help numpties like me. Have a happy and safe new year all of you and thanks again.