TRV 2 way

17 Oct 2008
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United Kingdom
Hello :) ,

I hope someone can help with a radiator problem we have.

My gas Combi boiler is a Vaillant Thermocompact. My hot water
works fine, but I have a slight *problem* with the central heating.

All my rads have TRVs (Myson TRV 2 way), each of these is set to their own temp per room. The only room that doesn't have a TRV on the rad is the hallway (where the house thermostat is located).

The TRVs have a settings that go from white circle to *, I , II, III, IIII and black circle.

The programmer timer on the combi boiler works fine as it should for both hot water and CH.

The problem is:

When we switch the house thermostat off (it clicks ok as it should), - the radiators still heat up even though the house thermostat is switched off.

The rads have continued to come on themselves with the house thermostat on zero.

Does anyone know what the problem could be? I would prefer to control the central heating using the house thermostat, as this seems to be wasting excess gas.

Is there a setting on the Myson TRV 2 way to override it so the radiators are forced to use the house thermostat, I thought maybe the white circle setting, hence the name TRV 2 way (or am I barking up the wrong tree?)

Or is this a bigger problem? :?: [/b]
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the trvs are not linked to yuor room stat , the room stat should turn the whole heating off when the temp is reached , so either the room stat is faulty or wired incorrectly.
Thermocompact is a system boiler, not a combi.

You probably have a stuck motorised valve.
thanks for the replies, I'm going to have the boiler serviced this month, so hopefully, the corgi guy should give it a good clean, and maybe sort the problem out
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Just got the boiler serviced today. The Corgi guy did some testing and believes its the motorised valve (Potterton MPE222) is getting stuck, as described in Simonds post.

The engineer removed the motorised valve off the plate and pipe, and had a look inside, and said he can't fix it, and we'll need a new one which is £100 inc labour and part. Is this value for money? :confused:

The symptons are, when the thermostat is turned up and clicks, the motorised valve spindle turns very slowly for a about 10 seconds and then goes off, when I turn the themostat all the way down the motorised valve spindle spins very fast for a few seconds then stops.

Even with the motorised valve device now removed from the pipe (electrics are still connected to device), the problem still exists as described earlier, the heat comes on even when the timer is switched off, and thermostat is on 0 degrees. Is this conclusively due to the faulty motorised valve.

Because if the motorised valve device is removed from the pipe, then it is effectively no longer turning the central heating on or off. Does the motorised valve device on its own send any feedback to the vaillant boiler, or is it's role only to take in electricity and turn the central heating on or off based on the temperature setting on the thermostat?

I said to the engineer, that if I manually turn the valve horizontally, can I use this as a workaround, he said no, as this will only turn the water off for the central heating, but the boiler will still come on.

Is there any way I can manually fix this without a new part
Thanks for your help everyone, I bought an act222 actuator for around £34, and fitted it myself, all is working now normally.

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