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Andrew Smith
Andrew Smith, Engineer
Category: UK Plumbing
Satisfied Customers: 3629
Experience:  Domestic Gas, Commercial Gas, LPG, Unvented Hot Water, Part P Electrical, Commercial Catering
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My central heating only comes on when the hot water is on and

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My central heating only comes on when the hot water is on and I suspect a valve problem. The hot water system is unvented and I have two 2-port motorised Honeywell valves labelled (by the installer) heating and hot water. Although we have only just started to have the heating on the problem has coincided with the replacement of a radiator and minor pipe rearrangement in the downstairs bathroom. The radiator has not yet been attached as we are waiting to decorate.
Hi my name is XXXXX XXXXX lets see if we can get you sorted in the shortest possible time. Can you check to see whether the 2 port on the heating opens itself and then "clicks" when fully open?
Customer: replied 5 years ago.
Not quite sure what you mean. I can move the lever but it moves back to its original position when I let go.
Does it go slack if you turn the heating on and turn up the room thermostat?
Customer: replied 5 years ago.
Yes, it's now slack.
Does the boiler fire now it is slack?
Customer: replied 5 years ago.
Yes, I just turned up the thermostat again, the boiler fired and I checked the lever which is slack.
Is this just with the heating on and the hot water off?
Customer: replied 5 years ago.
No with both on. If I turn the water off the boiler switches off. I have just checked the lever with the water off and it's no longer slack.
You are either wired wrong or the programmer is set wrong. The programmer should provide power to the room stat and then onto the motorised valve, which then opens and turns on the pump and boiler. What is the make of the programmer?
Customer: replied 5 years ago.
It's a Danfoss but has worked for the past 2 years or so. There have been no recent changes to the wiring or programming.
You may have a fault in the wiring center where the grey and orange wires connect or it could be a fault on the motorised valve head where it is not making the microswitch once it opens the valve. Check for loose wires in the wiring center (with the power off) first and if it is all ok, then swap the head on the valve.
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