Quick question: open vented central heating system, having probs right now, need to know if the pump (which is in the airing cupboard, just before the splitter valve (left to tank, right to heating) is instructed to turn on or off by the boiler or not? If not, please advise where it might be controlled from. Thanks tons, freezing nuts off without heating, Chris.
Does the boiler instruct the water pump?
- Thread starter cinman2003
- Start date
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you need to get into the junction box and check between neutral and orange s/live for240v. this is what will tell boiler and pump to start running if you dont have this then it is a good chance that you may have a problem with external controls stats timeclock etc
Appreciate the quick feedback - thanks tons - will check tonight and advise what I find 
You have a 3 port valve, which can take up any of three positions according to what you have switched on and whether or not the demand has been satisfied.
The pump is controlled in the same way as the boiler.
If 'hot water' is involved then the cylinder stat supplies the power.
If its just 'central heating' only, then its the room stat that supplies the power through the 3 port valve.
If you can't get CH only its most likely the valve/head at fault.
The valve has to move across to the correct position and trigger a micro switch.
Sometimes its just the motor in the valve head that needs replacing, but there are other things to consider.
Can you verify if the valve moves, or is it kind of stuck at HW position.
Within the head are 2 micro switches (2 way type) so 4 sets of contacts.
These contacts get dirty and burnt and sometimes don't make contact or don't break contact as and when they should.
If the valve head is found to be faulty then replacing it the best option.
With both HW and CH off there should be 230v on the valves grey wire (this is required to move the valve over the second section)
With CH on there should be 230v on the valves white wire (this is supplied by the room stat and is required to move the valve over the first section)
If the valve was in good working order there would be power coming from the valves orange wire which would then light the boiler.
The pump is controlled in the same way as the boiler.
If 'hot water' is involved then the cylinder stat supplies the power.
If its just 'central heating' only, then its the room stat that supplies the power through the 3 port valve.
If you can't get CH only its most likely the valve/head at fault.
The valve has to move across to the correct position and trigger a micro switch.
Sometimes its just the motor in the valve head that needs replacing, but there are other things to consider.
Can you verify if the valve moves, or is it kind of stuck at HW position.
Within the head are 2 micro switches (2 way type) so 4 sets of contacts.
These contacts get dirty and burnt and sometimes don't make contact or don't break contact as and when they should.
If the valve head is found to be faulty then replacing it the best option.
With both HW and CH off there should be 230v on the valves grey wire (this is required to move the valve over the second section)
With CH on there should be 230v on the valves white wire (this is supplied by the room stat and is required to move the valve over the first section)
If the valve was in good working order there would be power coming from the valves orange wire which would then light the boiler.
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MANDATE, just wanted to say thanks loads. It's all working now, albeit slow to heat up the rads (separate post). Many thanks for your valuable advice.
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