UFH zones come on at random - strange or normal?

[DevsAd]

Hi.

This UFH system is in my mil's bungalow purchased earlier this year.

It has 9 zones, is run from a WB 37CDi combi, and uses Wavin actuators with a wall stat in each zoned room. It all appears to work just as it should.

A few weeks back, tho', one of the two bedrooms warmed up excessively - it reached over 20oC and the floor was noticeably warm - even tho' the 'stat had been set to only 15oC. It 'clicked' at the correct room temp - 20-ish - but the heating wouldn't go off when turned back down. Just as I was starting to look at the system for the first time - and blowing my mind at what was behind the panel - it seemingly sorted itself, and I could see that the Wavin actuator was now working just as it should, and responded correctly to the wall stat, opening and closing slowly. Since the valves were working correctly, and also because I couldn't see the issue being caused by a 'sticking' valve, I, cough, put it down to 'user-error' - perhaps Nan had turned it right up the previous night, and was only noticing the delayed response in the morn after having turned it back down?

This morning, tho', Nan tells us that the spare room - wall 'stat kept at ~12oC - is hot and the 'stat clicks at 20oC. This is exactly what happened with the other bedroom. This really didn't make any sense - how could a zone come on that much by itself - unless it's a built-in anti-seize feature, perhaps? Is it designed to open up zones at random if they aren't being used?! If not, what on earth else could be causing this?

Thanks

 

[ShaunCorbs]

The yellow circles are air vents

No it shouldn’t be doing it’s own thing could be a few issues

I would test the stats first with a multi meter to see if there calling when there not supposed to eg next time it over heats a room etc

 

[DevsAd]

Thanks Shaun

(Sorry - the yellow circles are a red herring for this Q - that was for a different question when I wanted to know if they could be checked for air!)

Rats, so there's no timed valve/pump anti-seize? It's plumber-time, then.

It's so weird, because the stats clearly otherwise work as they should - click them up, and the valves open over a few minutes (which I understand is correct as they are wax?). And then they close reliably when the 'stat is turned back down again.

(Unless it's still user error and Nan is going into these rooms, turning them up, forgetting about them, and then turning them back down a few hours later...)

Cheers.

 

[ShaunCorbs]

No if there was would only turn on for maybe at most 5 mins if not used for a month etc

Yes correct or bi metal

It could be might be worth going round and setting them and putting a piece of tape on them to see if they are moved as tbh once set you shouldn’t have to move them unless there’s no timer on the system?

 

[DevsAd]

There is a normal programmer to set the times, but I've set that to 'on' 24hrs. I've suggested she considers the system to have a ~3-hour lag, so to turn her living space up to the required 'evening' temp at around 3pm, so it should be cosy for sitting down from 6pm onwards, and then to turn it down to 'overnight' setting - around 16oC - a couple of hours before bedtime.

If there's no anti-seize, then I wonder if system is just over-shooting when it does come on? Ie, if her bedroom dropped below 15oC, and the spare bedroom dropped below ~10oC, so the zones came on as they should - but then heated up the floor too much so that it continued to heat the air waaaay above the set temp even after the zone closed off again?

The main living areas certainly don't do this - they seem to come up to the required temp nice and slowly, and don't overshoot.

Could the bedrooms be receiving too much 'flow'?!

 

[ShaunCorbs]

Might be best to factor in the heat up time to the timer eg set for coming on a 1 if she wants it on for 4 etc

Once warm yes it might overshoot by a couple of dc unless someone has been adjusting the stat because don’t forget you will have the same 1 hour battery in the floor so will still give off a decent amount even when off could be the problem in a small room

 

[DevsAd]

Thanks.

I wonder if that is all that happened - it fired up that zone from cold, so by the time the air temp had reached the wall 'stat's setting and turned it off, the floor mass was already hot and just continued to chuck out the warmth until it was waaaay too high?

I can't think of anything else. For instance, these wax 'stats not only worked as I'd expect them too, but I can't see them 'sticking' in the open position in any case, only in the closed if anything? Ie, the wax stat part could open fine, but the 'plunger' could be left stuck closed (like a TRV), but I can't see how it could be stuck open - the 'stat 'cap' would still be sticking upwards.

Anyhoo, we'll just monitor it, and if it happens again she'll have to get someone in to have a look

Thanks for your help Shaun.

 

[DevsAd]

Lawdie.

With the help of a temperature scanner - an ex-Covid item - set to 'surface', we worked out that no less than 5 zones out of 9 were controlled by the wrong actuator heads. Heads now on correct valves, and all is working fine.

Lawdie.

(Can thoroughly recommend an IR temp scanner - from less than £10 - for tasks like this. It detected a ~0.5oC temp rise in a floor after only around 25 minutes, saving us numerous hours of waiting. Would also be ideal for balancing radiators, I'd have thought - a 'click' on the flow and one on the return tails.)