CH warms up then goes cold?

Joined
1 Jul 2006
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Something odd with my pretty new central heating setup, unless i'm missing something. Its a glow worm flexicom 30cx put in a year or two ago. The system heats up fine intitially but seems to keep going cold after a while. I have the CH set to max of 82 on the boiler. Thermostat is calling continually for heating and the receiver shows a green light. Boiler fires now and then to heat up otherwise is making whirring sound which i guess is circulation? There are only a couple of rads on two circuits and no airlocks. As i say heats up great at first but just goes cold even though everything looks like its on. Any ideas? HW works fine.
 
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Bit more detail please. Any trvs on the rads? Anyone been playing with lockshields or trvs? Where is the room stat, what is it set at?
 
trvs is thermostatoc valves? on all rads and fully open. Nothing else messed about with. Stat is in the hall.. i change it all the time to suit, but as above i'm not getting the heat it calls for. No prob with the stat or its connection to the boiler it's just that after an initial warmup it doesn't seem to maintain rad temp even though the stat is calling for it and the boiler seems to be firing to top up water temp.
 
Its the valves. I had thought 5 would mean it being fully open regardless but clearly not. The pipes are hot on the flow side. Guess i'll have to put a normal valve in here or take it off to have the room hot enough.
 
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So.. mark 5 on that trv (siemens activatix rtn51) is supposed to correspond with an ambient temp of 28deg whereas its closer to 20 (i brought the stat in and left it right by the valve for a reading). Maybe a defective valve?
 
So.. mark 5 on that trv (siemens activatix rtn51) is supposed to correspond with an ambient temp of 28deg whereas its closer to 20 (i brought the stat in and left it right by the valve for a reading). Maybe a defective valve?
Possibly. Do the same test with a couple of other valves.
 
Given that these have all been installed vertically anyway how well is it going to be able to read room temp anyway? (manual said they should be installed horizontally so convection from pipes doesnt warm the valve sensor)
 

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