The boiler is only heating water to the radiators when the hot water is being heated . I have changed the motorised 3 way valve, with no change ? could it be the roomstat or the programmer. The roomstat does make that click at low temperatures but does not fire the boiler. Does anyone have any ideas?
Central Heating only works only when heating water
- Thread starter Hunky Chunks
- Start date
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cylinder stat
The hot water does seems to stop heating when it has reached temperature ? how does this affect the central heating?
Well the room stat drives the 3 way valve to the mid position only by supplying power to the white wire of the valve.
The cylinder stat supplies power direct to the boiler, but it is like a two way switch. one input but two possible outputs. So when cylinder is satisfied it diverts the power from boiler to the grey wire of 3way valve.
This grey wire now drives the valve from mid position to CH only position and the valve triggers a microswitch which feeds power out through the orange wire to fire the boiler.
There seems to be some problems where the motor within the valve is faulty or the microswitch has failed, but if you have new valve then it could be a wiring problem.
In addition to the the wire from cylinder stat to valve (grey), there should also be a wire from programmer HW OFF terminal to connect with valve (grey).
This is because the cylinder stat wire would not be live if HW was switched off and this HW OFF wire is to replace it and allow CH to operate alone.
So it looks like either the cylinder stat or the wiring.
What happens when you try CH only?
The cylinder stat supplies power direct to the boiler, but it is like a two way switch. one input but two possible outputs. So when cylinder is satisfied it diverts the power from boiler to the grey wire of 3way valve.
This grey wire now drives the valve from mid position to CH only position and the valve triggers a microswitch which feeds power out through the orange wire to fire the boiler.
There seems to be some problems where the motor within the valve is faulty or the microswitch has failed, but if you have new valve then it could be a wiring problem.
In addition to the the wire from cylinder stat to valve (grey), there should also be a wire from programmer HW OFF terminal to connect with valve (grey).
This is because the cylinder stat wire would not be live if HW was switched off and this HW OFF wire is to replace it and allow CH to operate alone.
So it looks like either the cylinder stat or the wiring.
What happens when you try CH only?
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Thanks, if I have only the central heating on, this does not come on , evrn if roomstat fires. Is it possible the plumber may wired the new 3 way incorrectly ? As there is a Honeywell connector box in the location of the hot water tank, to which the 3 way valve is wired, along with the pump. cheers
Make sure hot water off from programmer is connected to Grey from mid pos valve and normally open (terminal 1) of cyl stat.
If the grey in the terminal box is live when selecting CH only, then I would suspect the motor or microswitch within the actuator head.
Try selecting both HW and CH, this should put the valve in mid position. ( which I think it will be doing, as you do get some heat to the rads )
Then turn off the HW and listen to the valve motor,you may hear it move to CH only position. If it does then I would suspect microswitch,If it doesn't I would suspect motor.
There is one other point worth checking out on the wiring.
The valve supplies the power to the boiler through the orange wire so check this for being live when selecting CH only. If it is live then wire from orange terminal to boiler must be faulty. If it's not live, then your looking at microswitch, motor or 'grey wire' suppling power to valve
Also faulty wiring could be something quite simple, terminals screw on wire insulation instead of bare wire or inadequatly wired
Try selecting both HW and CH, this should put the valve in mid position. ( which I think it will be doing, as you do get some heat to the rads )
Then turn off the HW and listen to the valve motor,you may hear it move to CH only position. If it does then I would suspect microswitch,If it doesn't I would suspect motor.
There is one other point worth checking out on the wiring.
The valve supplies the power to the boiler through the orange wire so check this for being live when selecting CH only. If it is live then wire from orange terminal to boiler must be faulty. If it's not live, then your looking at microswitch, motor or 'grey wire' suppling power to valve
Also faulty wiring could be something quite simple, terminals screw on wire insulation instead of bare wire or inadequatly wired
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