Central heating thermostat

[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?