3 way valve problem

15 Oct 2011
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United Kingdom
I'm helping out with a heating system which hasn't been used for a while (empty properrty). Hot water works, but no Central Heating. The system is Y plan with timer controlling both HW and CH and stats controlling HW and CH independently. I changed the circulating pump (original leaking and corroded replaced with Grundfos 15/50), still no CH. I changed the 3 way valve (original having no manual over-ride capability with Honeywell V4073A). I now have:
HW when called for,
CH when called for as long as HW is also called for,
No CH when HW not called for.
When the valve should divert to CH only I get a ticking (sound like microswitches being activated/de-activated) and no sign of the circulating pump or boiler turning on. I am able to select CH using the manual setting on the valve.
Could there be a fault with the new 3 way valve, or is there a chance that the wiring was not connected correctly (I have connected like - for - like)?
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Been a few years since I did one but as I recall when the c/stat switches off H/W, power is then supplied to the grey wire in order to move the valve past it’s mid stalled position.
Sounds like it may be trying to motor over but is not getting power to complete the move.
Be worth checking the c/stat is switching power to it’s off terminal when satisfied.

Hope it helps.
Thanks footprints and scatmanjohn, I have discovered that the system was using a Danfoss 103 which is single channel so have replaced it with a Honeywell ST699. Fingers crossed I should be able to sort the problem.
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The valves grey wire needs two sources of power. Agreed the cylinder stat does divert the power when HW is satisfied and this drives the motor/valve over the last half of the range. But this is of no use if HW is not on.
So to overcome this problem a wire is taken from the HW OFF terminal to join the wire from cylinder stat

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