Broken thermostat - options

cletus

So, I have two towerstat rs thermostats in my house. One controls upstairs, and one downstairs. In the hotpress I've two motorised valves, again one for upstairs heat, and one for downstairs. All the radiators have TRV valves installed

Subsequent to moving into the house, I had a Nest thermostat installed, so the two towerstats were set and forget.

Recently, the upstairs towerstat stopped working. I tried to get a like for like replacement, but I've struggled to find a shop with an analogue 3 wire stat in stock (the EPH CM3 seems to be the one I want, but not available anywhere I've checked)

I was given advice to manually override and temporarily disconnect the motorised valve for upstairs. I've done this, which is allowing me to heat the bedrooms tonight.

My question is, considering the TRV valves in every room, can I leave the motorised valve permanantly disconected, removing the need for the stat on the wall upstairs, and simply set the TRV's in each room appropriately?

10-10-20

https://www.boards.ie/discussion/2058275817/broken-thermostat-options

In theory, yes. But you lose the zoning. My stats are set at 30 degrees with digital TRV's to control the temperatures - so same difference, but I can still close off the zone.

The other thing which you lose is the ability of the valve to close off the zone when there is no call for heat. That can create pressure issues when all of the TRV's are closed off but the boiler remains running.

cletus

When you say close off the zone, do you just mean turn down the stat?

I take your point on the the pressure with no call for heat

10-10-20

https://www.boards.ie/discussion/comment/119998096#Comment_119998096

Yes, close the zone by turning down the stat. 👍️

cletus

Ok, just to come back to this.

I have the thermostat installed, heating is working, but there seems to be an issue with nest controlling the heat.

Prior to my issue, downstairs wall stats was just set so they wouldn't turn the heat off (25+°), and upstairs stat was usually left off, as it wasn't needed most of the time.

Now, even if I turn the nest down, I also have to turn the wall stat downstairs off for boiler to stop running. When the heating comes back on with nest, I have to turn the wall stat up to get it to kick on.

Has turning off the power for the heating system reset something? Do I need to factory reset the Nest to get it to control the heat again?

Any ideas or suggestions most welcome

youtheman

With zone valves (normally) the only thing that tells your boiler to fire is when it senses any zone valve open. So if your thermostat is broken then you manually tell the boiler to fire by opening the zone valve with the lever. The only issue is that if you leave it open too long then there is the possibility that the water in the tank becomes too hot because you don't have the thermostat to tell the boiler that you have reached the set temperature point . Also you are relying on your 'pump overrun thermostat' to stop the boiler if the return temperature gets too hot. Will work, but not ideal long terms.

As an aside, you should not have a TRV is a room where any thermostat is located. You can't have 2 separate devices trying to control the temperature.

cletus

Thanks for that. I think I have it solved. I reset the heat link, all seems good now.

Edit. Scratch that, still the same situation as above

cletus

Ok, to come back to this once more.

I've been checking various components of the system, and it looks like the motorised valve for the upstairs rads is not working.

When I turn on heat for upstairs, the light comes on (it's an EPH valve head, not sure the model, but one of the newer ones you can simply disconnect from the valve), but no heat.

When I push the manual override switch with the heat on, it's stiff, and if I hold it open, hot water starts to to pass through the valve. I believe if the valve was opened by the motor, the override switch would feel loose or floppy.

So, I've seen online that sometimes, even though the motor is not working, the microswitch controlling it can be stuck in the "on" position.

How likely is that, and if it was the case, would it be a reason for my boiler turning on even though both stats are off?

10-10-20

That sounds possible, the switch could be stuck.

You can do a test: With the heating system isolated at the fuse/switch and as per the diagram 5.2 on this document, locate where the valve is wired back to the boiler. Break the loop which calls for heat by detaching the Grey wire and secure it temporally.

https://www.ephcontrols.com/wp-content/uploads/2017/05/20221101_A1P_DS_PK_Email.pdf

Next, power back up and see if the same problem exists.