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Andrew Smith
Andrew Smith, Plumber
Category: Plumbing
Satisfied Customers: 3591
Experience:  City and Guilds qualified plumber
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I have a potterton pro-max combi boiler and its controlled

Customer Question

I have a potterton pro-max combi boiler and its controlled by a Honeywell HCW80 wireless thermostat. We've recently had problems with the hot water and have just had to have the heat exchanger changed. However, on top of that our thermostat stopped working over Christmas and for a while we were only able to turn the heating on via the thermostat's receiver box next to the boiler but had no control over the heat at all. We have now purchased and received a replacement HCW80 and have done the teach-in. It all seems to be communicating properly, turn the thermostat on so the red light comes on, green light comes on on the receiver box, heating indicator light comes on on the boiler and after a while it fires up but therein lies the problem, it just doesn't seem to stop firing unless we turn the thermostat down so the light flashes and it turns it all off. We have underfloor heating in the bathroom and the control panel for this is near to the heating thermostat. They have always been pretty much in line in terms of the temperature shown on the control panel. Now the panel is showing a temperature of say around 18.7 degrees and the boiler is firing on all cylinders even though the thermostat has only been set to 17 degrees. What is up with this? My usual plumber isn't familiar with the HCW80 so didn't really give me a straight answer but to me it definitely isn't right, in my opinion once the hallway is heated to 17 degrees the boiler should stop firing and then fire up again when the temperature drops, or am I mistaken? I have tried resetting the boiler and thought this had solved the problem but five minutes later the boiler was firing up again. Please can someone help me?? Thanks
Submitted: 2 years ago.
Category: Plumbing
Expert:  Andrew Smith replied 2 years ago.

Andrew Smith :

If the thermostat is saying go and the boiler is firing, what is the problem - does the stat not turn the heating off again?

JACUSTOMER-ytvkfu6a- :

Yes, it just seems that the boiler is constantly firing even though the room temperature has been reached

Andrew Smith :

Does it turn off again if you turn the boiler onto hot water only?

JACUSTOMER-ytvkfu6a- :

Not sure, I will go and try now....

JACUSTOMER-ytvkfu6a- :

Yes the boiler stops firing when I turn the hot water off. It does stop firing but we have to physically turn the thermostat down to a very low temperature. Always used to just set it to 17 degrees in the evening and the boiler would fire up, reach room temp setting then stop firing and only fire up now and again, just seems to always be firing at the moment

JACUSTOMER-ytvkfu6a- :

Sorry when I turn the hot water only on!!!

Andrew Smith :

Are you sure it does not think the tap is running all the time?

JACUSTOMER-ytvkfu6a- :

I've just run the kids bath, the boiler is currently off as the house has got too warm so I have turned the thermostat right down to stop it firing, I;ve just checked the boiler and it is not doing anything, so it has just fired up to run the hot water for the bath but has gone off again. Surely if it thinks a tap is running all the time it will be firing all the time? It just fires continuously when the heating is on, doesn't seem to register that the temperature on the thermostat has been reached......is there a way of fixing this? The instruction manual for the thermostat is very basic.........

Andrew Smith :

Does it continue to fire when the thermostat temperature is reached?

JACUSTOMER-ytvkfu6a- :

Yes, in fact, we only ever turn the thermostat to either 17 or 18 degrees, it fires once the temperature is showing 18.4, which is a small fraction so maybe there is a slight difference between the digital display and the HCW80 but it fires when the digital display shows 19.0 degrees and the thermostat is set at 17, surely that isn't right? Before we had the problem with the hot water, the temp was reached and the boiler would cut out and as the house stays warm if we got a bit chilly we would have to knock it up a degree to get it to come on....just seems that since the old thermostat packed in something has gone skewed with the communication....

JACUSTOMER-ytvkfu6a- :

Sorry I meant to say it continues firing once the temp is showing 18.4......

Andrew Smith :

Is that the set temperature or the room temperature?

Andrew Smith :

If you press the + or - button it will give you the set temperature

JACUSTOMER-ytvkfu6a- :

Unfortunately the HC80 isn't a digital thermostat, it simply has a dial which you turn up or down, it doesn't give a set temperature.....the digital display I speak of is from the underfloor heating control panel which is near the thermostat........we have had the HCW80 for nearly three years and never had a problem with it.......does something need resetting on the receiver box?

Andrew Smith :

Does it click when you turn it up and down?

JACUSTOMER-ytvkfu6a- :

No, it has an led light that comes on when you turn it up to let you know it is sending the signal, it then flashes for a few seconds when you turn it down and it has cut communication. It is run by radio frequency....

Andrew Smith :

I take it there is a dial that tells you the temperature it is set on?

Andrew Smith :

Are you relying on one thermostat for setting the temperature and another in a different position to tell you the temperature?

Andrew Smith :

Depending on location and even height above the floor the temperature can be as much as 4 or 5 degrees different

JACUSTOMER-ytvkfu6a- :

Yes the dial has lines and numbered 10 15 20 25 30 etc, so we turn it up to 17 as that always seems to be a good temperature for the house, feels warm but not too hot. The boiler thermostat is on one wall and the other thermostat is on the wall next to it, they are at a similar height though and not that far apart, temperatures have always seemed to be fairly consistent with each other until recently. Just seems strange that the boiler doesn't seem to automatically stop firing, but then I guess it could do as it is in the loft of our bungalow so I guess unless we sit in front of it and watch it we can't be 100% sure, just always seems to be going when it shouldn't be.....

Andrew Smith :

I always have trouble relying on RF thermostats, you cannot guarantee the signal gets through all the time. Nothing better than a wire

Andrew Smith :

The only way to be sure is to turn it up and down as you need it then pop your head up to see if it has turned off, or watch the gas meter to see if it stops turning

Andrew Smith :

Surely a wire is easy in a bungalow, just bring it down the airing cupboard?

JACUSTOMER-ytvkfu6a- :

Yeah, never had this sort of problem in our old house, this RF thing came with the house, seemed reliable enough but seems that when the old one broke it has just gone completely wrong and any instruction manual I can find is very vague!!! I think I will spend the evening watching it!! I guess we could get a wired one, easy enough as the thermostat is on a wall of a store cupboard so it could be fed down easily enough but I have just paid out £50 for this new thermostat so I am determined it will work properly :-)

Andrew Smith :

OK, keep watching it and let me know

Andrew Smith :

(bearing in mind that dial thermostats are only accurate to +/- 1 degree - so 18 degrees could be anywhere from 17 to 19 degrees. A digital one is accurate to +/- 0.5 degrees)

JACUSTOMER-ytvkfu6a- :

Right, ok, will bear that in mind, will keep an eye on it and come back to you. Thanks

Expert:  Andrew Smith replied 2 years ago.
If you respond when have observed it for a few hours I am sure we can work this out

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