Ideal Logic Combi 30 boiler and Danfoss TP500Si (Wireless) - heating not turning off when temp is reached

[JoRDillo]

Hi there. Sleep deprived newbie here after being woken two nights in a row to the house being the temperature of a sauna. I've had this boiler / thermostat combo for around five years with no issues.

The Danfoss thermostat (sited in living room) normally kicks in if below temperature (17) yet two nights ago it did not turn off after reaching 17 - the radiators all through the house were boiling hot and the room temp 24 degrees. However, the thermostat continued to show 17 and could not / would not turn the heating back down. I needed to switch the boiler off to stop the rads from heating further. I changed the batteries the next day and all seemed ok - it was switching on at 17, moving up to 19 when asked to, and then stopping. However, I was woken in the night with my bedroom radiator being burning hot and the boiler merrily boiling away, although this time it was only my room that seemed to be affected. This time, overnight, I had dropped the thermostat setting to 14, knowing it was unlikely to kick in, yet it did. Again, I could not turn it off via the thermostat and needed to turn the boiler off.

Is it possible that I've inadvertently caught the programmer panel, that's located in the boiler cupboard next to boiler? Or do I have a faulty thermostat? All advice welcome and I'm very grateful. Thank you.

 

[dilalio]

Stuck relay in the receiver.
You could check operation with a multimeter or see if the unit has any LEDs that go on and off when a demand is made for CH on/off.

Or signal is being lost from sender unit. Some kit defaults to heating on when signal is lost, as frost protection.

 

[Deleted member 267285]

Is the thermostat showing a demand for heat?

 

[JoRDillo]

Thanks both of you. Chris, the thermostat will show demand for heat if I increase the temperature, so it responds then. But there seems to be no upper limit - it's not stopping itself at the desired temperature. It worked all day yesterday just fine, then seemed to switch itself on again in the night (despite only being set at 14) and burning hot and long.

Dilalio, so I could get one child to watch the panel unit by the boiler as I turn the thermostat up?

 

[Deleted member 267285]

Thanks both of you. Chris, the thermostat will show demand for heat if I increase the temperature, so it responds then. But there seems to be no upper limit - it's not stopping itself at the desired temperature.

What I’m asking is, say it’s set at 14 degrees, but continues to heat, is it the thermostat that shows a demand (little flame symbol) or is it just the boiler?

 

[JoRDillo]

Ah gotcha. No, no flame or demand. It's as if the thermostat assumes that the right temp is reached. So if the thermostat was showing 14 (whilst the boiler and radiators are getting hotter and hotter) and if I pressed the UP arrow on the thermostat, the little flame symbol would appear at 24 (which would be the accurate temp of the room).

 

[Deleted member 267285]

Ah gotcha. No, no flame or demand. It's as if the thermostat assumes that the right temp is reached. So if the thermostat was showing 14 (whilst the boiler and radiators are getting hotter and hotter) and if I pressed the UP arrow on the thermostat, the little flame symbol would appear at 24 (which would be the accurate temp of the room).

Glad you got there . Doesn’t seem like it’s the room thermostat then, not ruling it out altogether, but seems more likely the diverter valve inside the boiler.

 

[JoRDillo]

Is this something any boiler man can do, Chris? I appreciate your help, btw

 

[ianmcd]

post a pic of the display on the thermostat and the display on the boiler at the same time as the boiler is running when it shouldnt be

 

[JoRDillo]

Hi Ian. Will do. I'll go and see if it does it now. Bear with me!

 

[DetlefSchmitz]

We really need to see the light on the receiver at this time too. I assume the receiver is external to the boiler.

 

[ianmcd]

We really need to see the light on the receiver at this time too. I assume the receiver is external to the boiler.

Unless the OP has stated the wrong thermostat he has an SI not an RF so no receiver

 

[DetlefSchmitz]

Unless the OP has stated the wrong thermostat he has an SI not an RF so no receiver

Good point.

 

[JoRDillo]

I have 'something' in the boiler cupboard that's linked to the Danfoss wireless panel downstairs. The boiler and thermostat are currently behaving which is so frustrating...yet nice too....but I know that it'll go wrong any moment. Here are the pics of the thermostat and the one located by the boiler. I may have to wait a while for things to go awry with the heating. It was fine last night and then just decided to heat up in the middle of the night.

 

[Deleted member 267285]

Is this something any boiler man can do, Chris? I appreciate your help, btw

Most boiler repair engineers should be able to yes.