Is there a Programmer or Thermostat I am not aware of?

Joined
27 Sep 2012
Messages
21
Reaction score
0
Location
Ayrshire
Country
United Kingdom
For some reason my Central Heating boiler is firing up and heating radiators when the Thermostat is not calling for heat.

My set up is as follows:-
Boiler: Potterton Suprima 60L
Programmer: Myson MEP 2 … heating set to “On” constantly, water set to “auto” coming on in the morning and then again around tea-time
Programmable Thermostat: Honeywell CM907 in hallway ... set to “Auto” for selected times and temperature (21C)
Heating: Honeywell Motorised Zone valve … is at “Auto” setting doesn’t appear to be a problem
Hot Water: Drayton Zone valve … is at “Auto” setting doesn’t appear to be a problem
Radiators: TRVs on each except for the radiator in hallway (nearest Thermostat)

The problem is that my boiler kicks in and some of the radiators become very hot making the associated rooms hotter than hoped for.

This is inconsistent but usually occurs late in the evening and I end up having to switch off my boiler at the mains which is obviously a concern because no heating at all during the night and waking up to a colder house than I would hope (via the Programmable Thermostat).

One time that this happened, I changed the setting on the Myson MEP Programmer to “off” for both the central heating and water heater but the Bolier remained fired up and radiators heating.

The Programmable Thermostat room temperature reading in the hallway is going above the 21C setting (because the radiator is hot) but the thermostat is not calling for heat i.e. the little flame icon is not illuminated as expected, therefore I don’t think this is the problem.

The zone valves in the cupboard next to the water tank seem OK too … both in Auto position.

I had thought maybe a problem with one or more TRV but I thought that with the Programmable Thermostat not calling for heat and the Programmer on the “off” position then these would override the TRV.

Is there another thermostat, switch or programmer on the boiler that could be the problem?
 
Sponsored Links
You might have a frost stat wired in, normally only done when the boiler or part of the pipework is in an outbuilding or garage to prevent freezing it will be set at a few degrees above freezing to kick the boiler into life over-riding any other heating controls except the boiler thremostat it's self.
 
Zone valves micro switches/heads may be faulty. Check their operation with multimeter as they may be calling boiler
 
Zone valves micro switches/heads may be faulty. Check their operation with multimeter as they may be calling boiler

Thank you for the suggestion, I'll see if I can borrow a multimeter and check if there are any online guides for what I should be checking.

I also read that something may be sticking and I have moved the lever back and forth a few times and so far so good (has stopped calling for heat).
 
Sponsored Links
I have moved the lever back and forth a few times and so far so good (has stopped calling for heat).
The motorized valve is sticking.

You can normally remove the actuator (metal box), so the valve spindle is accessible. The spindle should turn easily by hand (normally about 20 degrees). If it is stiff, try using some silicon lubricant.

You also said that the rads were getting too hot. As you have TRVs on all rads but one, this means the TRVs are not working correctly; probably sticking. Remove the TRV heads (set them to Max first) and use something hard to press the spindle down. It should go down easily then spring up when released. Silicon lubricant can help here as well.
 
I would agree with DH about the motorised valve but the rads getting too hot, with trvs, I would suggest dirt in the valves which will not be solved with lubricant, they will more likely need replacing.
 
Zone valves micro switches/heads may be faulty.

Please note I made a mistake in my set up, the heating is controlled by a Myson MPE222 two way valve (doh!)

I haven't had a chance to check with a multimeter yet but I did take the Actuator/Head off the two way valve and the spindle is OK.

When the hating remains on the "Operating" light on the valve is not lit up but the valve was in the "open" position (loose). I read elsewhere that when there is a fault with the microswitches that is the case. Last night when the heating was being called I "chapped" the Actuator head and the actuator physically moved back to the Auto position and Closed.

The system was working as expected this morning ... heating came on as per the Programmable Thermostat and the two-way valve is closing when not being called upon.

s there any way to fix the micro switches or lubricate the gears/motor or is it a goner and need to replace the Actuator head? I have seen these for approx. £40.
 
When the heating remains on the "Operating" light on the valve is not lit up but the valve was in the "open" position (loose). I read elsewhere that when there is a fault with the microswitches that is the case. Last night when the heating was being called I "chapped" the Actuator head and the actuator physically moved back to the Auto position and Closed.
The contacts on a microswitch can weld together, which means the switch will be closed when the valve is open or closed. But there is no way a faulty microswitch can cause the valve to open.

If the valve was open (presumably lever loose) when it should be closed, then either the valve is sticking or the valve is receiving power when it shouldn't.

What's "chapping"? Do you mean you gave the actuator a thump?
 
Not quite a thump but yes a couple of hard chaps with my hand
That's a new one to me. ;)

If the spindle is free but the valve still sticks, then the actuator must be the problem. Check the gear wheels etc for damage. It may mean a new actuator.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top