central (overheating)

oldhand

I have a recurring problem with a motorised valve opener (best way I can describe it) on my central heating.Its job is to open the valve when the thermostat calls for it and close it again when the temperature is reached.The central heating is a "zone system" ie you can set it to heat upstairs only,downstairs only or both and this is controlled by these motorised valves (2 of them)one for up and one for down,theres also a third for the water heating for baths etc. These 3 motorised valves are grouped together behind a panel in the downstairs bathroom,now the problem,the valve for the downstairs heating keeps failing and when it does it remains fully open so that even when the thermostat is telling it to close its heating at full power and the only way to stop it is to switch it off at the main power switch which of course also turns off the other valves.Now it is always the downstairs valve fails,this will be the 5th one in 6 years replaced at £30 a time plus fitting,none of the others ever give trouble and they are all grouped together.The electrician who does the work cant understand it either,he told me the first time it was overheating so I cut a square out of the panel at the motor to allow more air at it.when the 4th replacement failed I cut 2 inch holes from top to bottom in the panel leaving it looking like a swiss cheese hoping that would let enough air to circulate but again it has failed.Both the electrician and I cannot understand why its always the same motor as the other 2 are identical and they never fail,the pipe work to all 3 is the same,I notice on the motor the writing says max ambient temperature is 53degrees and I would expect the temperature behind the panel would be much higher when the water is heating which may account for the motor failing but again why only the same one? and if that is the reason why did the builder put them there like that in the first place? Bit of a ramble I know but if anyone else has had problems like this and has any ideas Id love to hear them,thanks in advance.

DVardysShadow

As you acknowledge that you are exceeding the ambient temperature rating, your real problem is why the other valves are not failing ... I suggest that you sort out an arrangement which deals with the temperature and gives an ambient of no more than 40degC.

roger196

Is the valve for the downstairs heating a two port motorised valve. looks like www.screwfix.com part number 94189 as opposed to a three port one which is part no 93941. Was the whole valve replaced,or just the top part or just the motor inside? If the whole valve was not replaced, the arm inside the valve maybe sticking and overloading the motor.
Another possibility is the wiring may not be correct. There can be a lot of very funny wiring variations as in the early days many installers had their own strange versions. You will need a copy of the manufacturers instructions to track which colour wires go where in the ten way junction box and then onto the motorised valves. Make sure you FULLY isolate the system before working on it ie remove the fuse.
Finally is it possible to locate this motorised valve somewhere else and install a new one at the same time.

oldhand

roger196 wrote: »

Is the valve for the downstairs heating a two port motorised valve. looks like www.screwfix.com part number 94189 as opposed to a three port one which is part no 93941. Was the whole valve replaced,or just the top part or just the motor inside? If the whole valve was not replaced, the arm inside the valve maybe sticking and overloading the motor.
Another possibility is the wiring may not be correct. There can be a lot of very funny wiring variations as in the early days many installers had their own strange versions. You will need a copy of the manufacturers instructions to track which colour wires go where in the ten way junction box and then onto the motorised valves. Make sure you FULLY isolate the system before working on it ie remove the fuse.
Finally is it possible to locate this motorised valve somewhere else and install a new one at the same time.

many thanks for your reply roger,The motorised valve opener is a myson power extra,mpe222 as are the other 2 and it says on it 5w 27mA motor load,max ambient 52degreesC,water;5dg to 95dg&10bar.The complete motorised unit is replaced each time but not the valve inside the copper pipe,now its a qualified electrician does the work each time but your point about the arm which I assume is inside the copper pipe is something I never thought of and I will mention it to the spark as hes coming this evening to fit the new motor.thanks.

gas4you

These are terrible valves.

I would suggest replacing it with a Honeywell valve.

roger196

How's the repair going? It's always nice to know the outcome. This way one improves one's long distance diagnosis.