Underfloor heating wiring

dma0awc · Nov 7, 2021

I am a DIYr.

I have a gas fired underfloor heating system installed about 12 years ago. The controllers are Uponor C35 and thermostats T35 (there is also a UP36 mixer and outside sensor but I don't think that's relevant). There are two separate 4-port manifolds in different parts of the house. While doing some routine work. I noticed that when the thermostat calls for heat on one of the ports, not only does that actuator open but so does another - in the other manifold.

I can't figure this out from my limited understanding of how these systems work - I assume that the thermostat is essentially a switch and that it is only linked back to one of the C35s, so how can it affect the other?

Avo Mk8 · Nov 7, 2021

The interconnect between room stats and valves is normally achieved through a 'wiring centre' type base unit.
The Upnor one below shows more than one valve can be connected to operate from a single thermostat, so maybe what you have is by design? Or a wire in the wrong place!

[ElectriciansForums.net] Underfloor heating wiring

dma0awc · Nov 7, 2021

Avo Mk8 said:
The interconnect between room stats and valves is normally achieved through a 'wiring centre' type base unit.
The Upnor one below shows more than one valve can be connected to operate from a single thermostat, so maybe what you have is by design? Or a wire in the wrong place!
View attachment 91748

Yes, thanks Avo Mk8. But each manifold has its own wiring centre, and that's why I can't understand why the behaviour of one manifold would affect the other.

Avo Mk8 · Nov 7, 2021

dma0awc said:
Yes, thanks Avo Mk8. But each manifold has its own wiring centre, and that's why I can't understand why the behaviour of one manifold would affect the other.

Ah. OK. Is it possible this is by design, ie there is some rationale for the second zone being activated by the thermostat in question. Or does it make no sense at all from a heating perspective?
There must be a connection between the two, either deliberate or accidental.
Presumably all the thermostats are wired, not wireless (Could there be a 'pairing' issue)?

And just a thought - have you, or can you, establish if any other thermostat moves the second actuator.
On the same theme, does the thermostat that common sense would suggest operates the zone actually do so?

Do you think this is a feature that has always been present, or are you suggesting a fault has ocurred?
Sorry for all the questions ?

dma0awc · Nov 7, 2021

Avo Mk8 said:
Ah. OK. Is it possible this is by design, ie there is some rationale for the second zone being activated by the thermostat in question. Or does it make no sense at all from a heating perspective?
There must be a connection between the two, either deliberate or accidental.
Presumably all the thermostats are wired, not wireless (Could there be a 'pairing' issue)?

And just a thought - have you, or can you, establish if any other thermostat moves the second actuator.
On the same theme, does the thermostat that common sense would suggest operates the zone actually do so?

Do you think this is a feature that has always been present, or are you suggesting a fault has ocurred?
Sorry for all the questions ?

No problem, thanks for getting involved.

There would be no rationale in having it designed this way. All the thermostats are wired, and yes other thermostats also allow flow through the (same) wrong loop. But the thermostat always works its own zone.

As for your last question, it's difficult to say but I did discover some major wiring problems in the system a few years ago when one of the controllers burnt out (the installer has - perhaps unsurprisingly - gone out of business) which is why I've now jumped to the assumption that this is a wiring problem.

But I've just realised there may be another solution which is that the actuator on the 'rogue' loop is stuck at the open position. The pump is central so any thermostat would start pumping and if the loop was permanently open it would have flow through it, no matter which manifold it's on.

On reflection this seems like the obvious solution, so apologies for wasting your time on what might really be a plumbing rather then wiring issue. But - does this make sense to you?

Avo Mk8 · Nov 7, 2021

dma0awc said:
No problem, thanks for getting involved.

There would be no rationale in having it designed this way. All the thermostats are wired, and yes other thermostats also allow flow through the (same) wrong loop. But the thermostat always works its own zone.

As for your last question, it's difficult to say but I did discover some major wiring problems in the system a few years ago when one of the controllers burnt out (the installer has - perhaps unsurprisingly - gone out of business) which is why I've now jumped to the assumption that this is a wiring problem.

But I've just realised there may be another solution which is that the actuator on the 'rogue' loop is stuck at the open position. The pump is central so any thermostat would start pumping and if the loop was permanently open it would have flow through it, no matter which manifold it's on.

On reflection this seems like the obvious solution, so apologies for wasting your time on what might really be a plumbing rather then wiring issue. But - does this make sense to you?

Yes, you may well have hit on it. I suppose a test might be to turn everything off, and see if the rogue actuator closes. ?

dma0awc · Nov 7, 2021

Avo Mk8 said:
Yes, you may well have hit on it. I suppose a test might be to turn everything off, and see if the rogue actuator closes. ?

Yes thanks again that's it. See photo (there are actually two 'rogue' actuators I was just trying to simplify the description). I'm tempted to use WD40 and a hammer but I guess I should actually replace the pins.

Avo Mk8 · Nov 7, 2021

Good conclusion! WD40 isn't actually a good long term lubricant, and I suspect there may be other dodges.
You could try Plumbers Forum for further advice on the actuators.

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