Central Heating Motorised Valve Problem

Lance Vance

I have a problem using the thermostat to control the central heating in my house. When the desired temperature is reached on the thermostat the radiators remain on. I believe that there is a problem with the motorised valve.


The motorised valve is a Myson PowerExtra 2 port valve. http://www.myson.co.uk/products/1207_1421_ENU_HTML.htm
http://www.myson.co.uk/img/MPE222_Installation_sheet_Sept_2009.pdf


The motorised valve appears to be constantly open. I have tried the manual override but that does not close the valve. The connection between the actuator and thermostat appear to be working normally as changes in the thermostat cause the indicator light on the actuator to go on or off. I suspect that there is a problem with the mechanism which causes the valve to close. When it worked normally the lever on the actuator would move up or down, this no longer happens.


I plan to remove the actuator to see if I can solve the problem. When removing the actuator do I have to isolate electrics only or do I have to drain the heating system as well?

ntpm

Be careful as the motorised valve ( if wired properly) will have a perminent live feed. You will have to switch of the fused spur for the heating ( if wired correctly) or MCB in fuse board.

You can remove the head without draining the system. Replacement heads are available but you might only be able to buy the valve and body dependent in some suppliers.

You can replace the actuator motor only if you can buy it separetly. But imo quicker
and easier to replace the whole head.

Also to note:
The valve body must have jamed in the open position if the radiators are heating.
You may be able to take the head off, manually release the valve body and refit the head.
The body may have caused the head to fail. If this is the case then the system will need to be drained and the body replaced.
I would also suspect that the motorised valve/ system is not wired correctly ( boiler interlock) as normally a motorised valve that is jamed in the open position will cause the boiler to continually run ( if wired correctly).

Lance Vance

Thanks ntpm, I'll remove the actuator and see if I can fix it or if it has to be replaced.

Lance Vance

I removed the actuator. Thankfully there isn't a problem with the valve. The spring on the actuator must have seized in the open position. I was able to close the spring and the motorised valve is now working as it should.

ntpm wrote: »

I would also suspect that the motorised valve/ system is not wired correctly ( boiler interlock) as normally a motorised valve that is jamed in the open position will cause the boiler to continually run ( if wired correctly).

ntpm could you elaborate on why you think it is not wired correctly as I don't know much about heating systems (3 days ago I didn't know anything about motorised valves!). Thanks.

ntpm

Lance Vance wrote: »

I removed the actuator. Thankfully there isn't a problem with the valve. The spring on the actuator must have seized in the open position. I was able to close the spring and the motorised valve is now working as it should.



ntpm could you elaborate on why you think it is not wired correctly as I don't know much about heating systems (3 days ago I didn't know anything about motorised valves!). Thanks.

Basically the 2 port m/v has the following cables:
brown- Live - switches on/ off via the thermostat
blue- neutral cable
green - earth - not all motorised valves have this.
grey- perminent live- feeds an internal switch
orange - boiler live- output of internal switch

The time clock/programmer switches on a spaecific zone ( Either hot water or heating( upstairs or downstairs etc). This feeds power to the room thermostat which then sends power to the motorised valve. As the motorised valve fully opens it makes the internal switch. This internal switch then sends power to the boiler to run ( Boiler Interlock).

If the motorised valve was stuck in the open position the internal switch would be continuosly "made" respective of the programmer and this would cause the boiler to run continously.

The above explanation complys to Building Regulations Part L. (Energy efficiency regulation which came into existance around 2000, yes 10 years ago!!).
In my experience you will probably find the m/v grey and orange wires cut or not used.:(

davelyn

Lance Vance wrote: »

I have a problem using the thermostat to control the central heating in my house. When the desired temperature is reached on the thermostat the radiators remain on. I believe that there is a problem with the motorised valve.


The motorised valve is a Myson PowerExtra 2 port valve. http://www.myson.co.uk/products/1207_1421_ENU_HTML.htm
http://www.myson.co.uk/img/MPE222_Installation_sheet_Sept_2009.pdf


The motorised valve appears to be constantly open. I have tried the manual override but that does not close the valve. The connection between the actuator and thermostat appear to be working normally as changes in the thermostat cause the indicator light on the actuator to go on or off. I suspect that there is a problem with the mechanism which causes the valve to close. When it worked normally the lever on the actuator would move up or down, this no longer happens.


I plan to remove the actuator to see if I can solve the problem. When removing the actuator do I have to isolate electrics only or do I have to drain the heating system as well?

HI. In my view Myson valves are pure rubbish My house is five yrs. old and has 4 zones in the heating each controlled by a myson valve In those 5 tyrs all the valves failed and have been replaced mainly for faulty microswitches.. now the valves are failing again this time i'll replace the whole unit for a different type

marko99

I've also experienced a number of problems with these Myson MPE222 motorised valves. In my experience, it has always been the microswitch (boiler interlock) which has failed. I have replaced two heads already and the third one (HW) is now sticking constantly, so that the valve closes but the boiler keeps running. Good thing there's a bypass... I have to go upstairs and hit it sharply a few times to release the microswitch to get the boiler to turn off.

Anyway, after all that, my question is : Is it possible to open the head and perform any maintenance on the microswitch to stop it from sticking?

davelyn

Exact same problem i was having, they can be opened you may have to drill out a few tamper proof screws as far as i can remember . but the best job is to throw them out and replace them with a different brand. I have replaced all mine with honeywell and 2 yrs. on have had no trouble with them.

marko99

Ok thanks Davelyn - I presume you also had to change the valve though so that means draining the system etc?

Mine are about 11 years old and the current problem is the third of three (two have been replaced already). I still have the last faulty one I replaced so might try opening that and see if I can make sense of the innards...

davelyn

Yep. you will have to drain the system to replace the whole valve ( a job for the summer) it might be possible to get a better quality micro switch good luck with it.

marko99

davelyn wrote: »

Yep. you will have to drain the system to replace the whole valve ( a job for the summer) it might be possible to get a better quality micro switch good luck with it.

UPDATE:
I've since bought and fitted a new direct replacement. On opening up the faulty one, the problem is that some of the plastic has become brittle and has cracked (presumably due to the heat) so that one of the screws which holds the valve motor in place no longer "bites". This means that the torque caused by the valve opening causes the whole assembly to twist a bit so that the contact for the microswitch is broken. It would be difficult to fix.

whowantstwoknow

Hi,

I too now seem to have a similar problem with the CH value getting stuck open and keeping the boiler on. The value itself seems fine it just seems to be the actuator. For example took the head off and noticed in testing the actuator didnt return to the closed position

value must be 7 years old. Had danfoss values previously and they were a complete nightmare with the value leaking. So upon putting in the myson's had plumber install 3 manual values across the t junction so the system wouldnt need complete draining for subsequent value replacement.

While I could consider another brand I think it would be more cost efficient to purchase and replace the actuator myself...

W.

marko99

It's a very straightforward job to replace the actuator head so long as the valve itself is working ok.