heating coming on when hot water only selected

12 Jul 2007
Reaction score
United Kingdom
Fully pumped central heating system with 3 port danfoss valve. When hot water only selected radiators coming on also. ab, b and a pipework ports are hot. Motor recently replaced. The lever does not seem to go all the way to the hot water position on the valve. Would it benefit the system replacing the valve body and keeping the same motor. can there be a fault with the valve body itself.
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Try turning the valve spindle with tha actuator off. Do you know which end the manual lever should be when in DHW mode only? Valve rests in DHW setting, fully over the other end is ch only and about 1/2" from ch position is DHW and CH.

I would fit a new head if spindle turns ok.

Didn't realise you could change just motor on Danfoss, thought this was just Honeywell.
the lever seems to rest just before hot water only. (this i assume is why heating comes on when hot water only selected on programmer) When the actuator is off cannot seem to push the lever fully to hot water only. Could there be something preventing this on the valve itself.
:confused: When actuator is 'off' it should rest in dhw position. If you push the manual lever it will or should go to both dhw and ch position.
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Valve is letting bye, caused by either a worn out unit or more likely sludge in system, the operating spring is very weak and is easily held open by debri in the pipework, if the problem is intermittant it points to sludge as this may or may not be in the valve when it is trying to close.

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