Heating not working, maybe a thermostat problem.

[Silvan]

Hi all,

My system is the older kind with a hot water tank (not the hot water heated on demand type).

Hot water is working okay. All the heaters in the house have suddenly stopped working. I put my hand on the inlet pipe to all of the heaters and none of them feel warm.

The main thermostat seems a bit iffy. When turned from the lowest position to the highest position there used to be a single clicking sound at (e.g.) 18 degrees, then the heaters would start to warm up. Now when turned from the lowest position to the highest position there is sometimes a repeated random clicking sound at various positions as I turn the dial. Sometimes it goes right up to 30 degrees before the clickety-clickety-clickety happens. I suspect the bi-metallic strip which I assume is in there somewhere. The thermostat is hard wired not Bluetooth or Wi-Fi.

If it is likely to be the thermostat can I change it myself? What voltage might it be and how can I tell? Might it just be dust in there that I could blow out?

Pictures attached. Boiler is a Greenstar it is 15 or more years old. Heating controls also 15 or more years old. The thermostat is mode by Drayton.

Kind regards

David

 

[Silvan]

Hi, I am the OP. I gave the thermostat a few taps with my finger and now it is clicking in the appropriate way when I turn the dial. But my heaters are still not warming up.

 

[Mister Banks]

Change the thermostat after isolating power to the heating system. It’s a very easy and cheap thing to do.

 

[CountryFan]

Hi, to test the voltage you need to test between a neutral or Earth and switch live out which should be 230/240vac. If that’s functioning correctly then it’s likely the motorised valve.

 

[Silvan]

Hi,

Thanks for the help. Testing live electrical stuff is a bit out of my depth. I've attached some images of the motorised valve and an electrical switch.

(1) The electrical switch in the picture is located next to the boiler and when switched off the boiler goes off and the words on the adjacent control unit go out. Will that switch also switch of power to the thermostat and the mortised valves?

(2) The motorised valve has a manual operation lever. If I were set the thermostat to 25 degrees, then move that manual operation lever to OPEN, then use then use the heater controls to ask for heat would that help with troubleshooting? If the heaters warmed up then it is likely the motorised valve that is at fault? If the heaters do not warm up and the pump does not start then it is likely to be the thermostat? (see the second half of this video for manual operation of the motorised valve:

).

The valve was replaced 7 years ago. I remember that the faulty valve that was removed had a broken bit rattling around in it. If I unclip the motorised valve and shake it then a rattle would indicate a fault, right?

Thank for you help all.

 

[CountryFan]

There’s some guess work you’re trying here. No, placing the valve in the manual position doesn’t bring the heating on. Ideally you need to test, or replace the thermostat as the cheaper option first if you’re reluctant to call in an engineer.

 

[Tricky-Dicky]

Power off,
Change the room stat, (multiple clicking etc not good)
This looks to be the same stat:-

https://www.screwfix.com/p/drayton-rts1-1-channel-wired-room-thermostat/85263

If problem not resolved, then proceed further.

 

[Silvan]

Thank you I will try that. I had a look at the thermostat it has backplate with the wiring terminals and the actual thermostat unclips from the backplate. So the thermostat can be replaced without unscrewing any electrical wires making things very easy for me.

Out of interest, if the thermostat is okay and the motorised valve faulty what would happen to the pump? Would the pump be working and pushing against a closed valve if there were a call for heat?

Will try to get to screwfix this afternoon.

Many thanks.

 

[ericmark]

It depends how plumbed, some times the micro switches in the motorised valves fail, if three port valve latching lever into the bleed position sometimes will give a temp fix.

Valves do make a small noise, so turning thermostat and listening or feeling valve to see if the lever becomes loose, or sound heard may help.

 

[Silvan]

Hi folks.

I got a new thermostat but the problem remains.

When I turn the dial on the thermostat there is no clicking noise. Could this be a problem with the thermostat not getting power at all? In the fitting instructions it says that a 3amp fuse should be fitted which I will look for.

I had a look at my motorised valves. When I switch on the hot water the indicator on one of them goes to from A to B, and the lever on top moves position. But when I switch the heaters on there are no changes to the other motorised valve (the indicator stays on A).

What to do now?

 

[CountryFan]

What to do now?

Could be the programmer not sending voltage to the thermostat or the motorised valve not engergising. I would be testing for voltage, but since it’s out of your comfort zone, maybe call someone in?

 

[Silvan]

Hi, Thank you.

I was wrong when I said that there is no clicking when moving the dial on the thermostat. If the control unit is set to ask for the heaters to be on there is clicking when it is rotated past the room temperature.

At the present time I am thinking to get a new motorised valve then call somebody in. If it is the motorised valve he or she can go ahead and fit it. If it isn't the valve I can take it back to screwfix. How does that sound?

 

[CountryFan]

I was wrong when I said that there is no clicking when moving the dial on the thermostat. If the control unit is set to ask for the heaters to be on there is clicking when it is rotated past the room temperature.

That’s good

At the present time I am thinking to get a new motorised valve then call somebody in. If it is the motorised valve he or she can go ahead and fit it. If it isn't the valve I can take it back to screwfix. How does that sound?

Sounds feasible. For the time being, the actuator (the white head that sits on top) is replaceable so you may only need to change that. You can remove the head (black tab at the side) and rotate the spindle - if it’s stiff whole valve, if not just the head. You can also do this and get a bit of heating when the hot water is being called for.

 

[Silvan]

Hi,

I took the motorised valve off and found that the brass spindle can be easily rotated using my fingers, but only by 45 degrees.

I also found that:

• when heat is called for the pump does not activate, nor does the motorised valve.
• if the main control unit (the one with the timers) is set to call for heat, the thermostat makes a clicking sound. If the control unit is not set to call for heat the thermostat makes no clicking sound. Does this mean that the main control unit is probably okay?
• with the motorised valve off the spindle if heat is called for the valve has no response (makes not attempt to turn the spindle).
• when I manually pushed the lever on the motorised valve to the open position the pump did not start.
• I took the back cover partially off the motorised valve and nothing fell out (a few years ago the other motorised valve failed due because a plastic bit inside it had broken).

Is it looking like the motorised valve is the main suspect? It is around 20 years old.

Many thanks

 

[CountryFan]

Seems to be pointing to the motorised valve head then - failed motor by the sound of it, or end switch.