Central Heating does not turn off when temperature on dial met

[Tyzerx]

Hi All,

this has been an issue for over a year now in a new house (obviously didnt use heating during summer) - so this could be set up is incorrect or something is broken - since i have moved in i have not known it to work.

We have a Glow-worm HXI18 Boiler, a Honeywell temperature dial and a digital unit on the wall (Potterton EP2001) near the boiler which allows us to set on and off times for CH and HW independently.

The issue i am facing is that we can set the dial (located on upstairs landing) to 15 degrees (which i presume if temp dips below, heating goes on, if above heating goes off). However the heating can turn on but it does never turn off - i bought a separate digital thermometer and places above the dial on wall (which doesnt have a screen) digital thermometer can read 19 degrees.

Clearly something is not working correctly but i would not know if this is due to settings in one of the three items above OR something is broken...

Is there a way i can test or amend settings to see what the issue is - any help is appreciated!

Thank you

 

[hertsboilers]

The most suspicious part is motorised valve, stuck.

 

[Tyzerx]

The most suspicious part is motorised valve, stuck.

Thanks hertsboiler I did read this somewhere - is there anyway to test this theory?

And I presume by motorised valve we mean this thing... (attached)

 

[hertsboilers]

That is a Danfoss three port, download its instructions manual, and if you have electrical test gear like multimeter or voltage tester, pretty easy for some engineers, otherwise call a professional.

 

[stem]

If you were to turn the thermostat dial up and down from max to min, you should hear an audible 'click' as it passes the actual room temperature value. Does this happen?

 

[Tyzerx]

If you were to turn the thermostat dial up and down from max to min, you should hear an audible 'click' as it passes the actual room temperature value. Does this happen?

Hi Stem, yes it does make an audible click it always seems to be around the same mark 12/13 degrees which doesn’t match up with the seperate thermometer as room temperature...

My initial thoughts (I have no background in this) was that the copper inside the dial could be broken? Or we have not got the boiler on the right setting potentially...)

Thanks for your help

 

[stem]

If it's wired properly, normally, the room thermostat supplies the motorised valve with power (via the white wire) when it calls for heat. (ie is 'on') This supply is also fed from the valve to the boiler, (via the orange wire) so when the room thermostat switches 'off' there isn't any power that can go to the boiler.

The programmer does the same thing, so when you turn off the programmer / timeswitch, does the heating go off then?

It may be that the thermostat is broken as you suggest (I assume that is what you meant by the copper inside the dial could be broken) and someone has joined the wires together inside so that it is permanently 'on' or that it is just faulty and is permanently 'on'

Can you open up the thermostat safely and post a photo of the wiring?

 

[Tyzerx]

Can you open up the thermostat safely and post a photo of the wiring?

Hi Stem, so I opened it up see attached before and after - the little white thing next to 20 degrees looks interesting almost like a marker?

So if I move the dial to a little less temp about a degree to the left the heating would turn off - room temp is 18 degrees, it would turn back on if I moved it back right by a degree or two which is well below room temp.

Heating will switch on when a poterrton ep2001 is timed to. But just doesn’t seem to take into account room temperature. House can get up to 24 degrees if I leave it! Like the Sahara dessert.

Anything you can see in the pictures?

Thanks for your help once again

 

[fezster]

so when the room thermostat switches 'off' there isn't any power that can go to the boiler.

I thought the motorised valve has a permanent live which would be fed to the SL of the boiler via the orange wire if the valve is stuck open or the microswitch is stuck. This is true of the honeywell valves, at least.

 

[stem]

Three port motorised valves don't have a permanent live, they have a switched wire from the room thermostat to put the valve in the heating position. When the live is removed it returns to the hot water position by a spring.

Two port valves do have a permanent live that feeds a microswitch that controls the boiler.

Tyzerex, I'll look at your photos shortly when I can see them better on my laptop.

That is a Danfoss three port

Is it though? I can't see properly, Tyzerex are there 2 or 3 pipes connected to your valve?

 

[Tyzerx]

Tyzerex, I'll look at your photos shortly when I can see them better on my laptop.


Is it I can't see properly, Tyzerex are there 2 or 3 pipes connected to your valve?

Hi Stem looks like it has 3 going into it - another picture to make it clearer...

 

[stem]

Yep that's definitely a 3 port valve. The thermostat wiring looks as I would expect. But as you have now informed us:

So if I move the dial to a little less temp about a degree to the left the heating would turn off

So in that case, the thermostat is controlling the motorised valve and it is working OK, the heating is going 'on' and 'off'. I thought when you said:

the heating can turn on but it does never turn off

I thought it wasn't going off when you adjusted the thermostat. So, therefore as you originally suspected, the room thermostat is the problem.

 

[fezster]

Three port motorised valves don't have a permanent live, they have a switched wire from the room thermostat to put the valve in the heating position. When the live is removed it returns to the hot water position by a spring.

Got it. Thanks.

 

[Tyzerx]

Yep that's definitely a 3 port valve. The thermostat wiring looks as I would expect. But as you have now informed us:
So in that case, the thermostat is controlling the motorised valve and it is working OK, the heating is going 'on' and 'off'. I thought when you said:



I thought it wasn't going off when you adjusted the thermostat. So, therefore as you originally suspected, the room thermostat is the problem.

Apologies with some of my explanation! Yeah it seems to turn on or off when I twist around this level of degrees, once on only way for it to turn off is to twist to the left OR turn off at the programmer. Temperature on dial being met doesn’t turn it off etc.

In terms of replacement what is the best solution for a reasonable price?

Thanks for your help Stem!

 

[stem]

I usually go for Danfoss, Drayton or Honeywell. The digital versions are battery powered and show the actual room temperature. Also, as they are solid state they don't become inaccurate over time. As with most things you get what you pay for. I have fitted a couple of cheap Salus thermostats, and not had any problems with them, but there are a few on here that aren't too keen on them.

Make sure you get a 'Room Thermostat' and not a 'Programmable Room Thermostat' which has the programmer functions built in. As you already have a programmer you don't need them.

The Honeywell you have is usually quite good for the money (about £20) and it is unusual to have a problem with them. You can still get one so it would be a straight swap. It's a Honeywell T6360B. Maybe the previous occupants gave it a bash with some furniture as they were moving out. The digital Honeywell DT90E is about £30.

If you do get a different thermostat and need any help swapping them over, post back.