Hot water cutting out the central heating

5 Apr 2006
Reaction score
United Kingdom
When I turn my central heating on by pressing the button on the programmer everything is fine, If I then press the button for heating the domestic hot water the pump and boiler switch off, the lights stay on at the programmer if I then turn off the Hot water the pump and boiler kicks in again to heat the rads..... can anyone shed any light?
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only stops when both ch & hw on ?

wot type of diverter valve have you , suspect a 3 port .

wired up wrong , hw off signal not present ?
yep the ch is on, then turn on hw, then it shuts down until hw is turned off then ch comes on again

Yep a 3 port honeywell with potterton programmer
Either the system is wired up wrongly or the diverter valve has failed.

Has it been fiddled with or did it just stop working?

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Well, 2 weeks ago I cleaned the system and added Fernox, when draining I put the 3 port valve on manual...thats about it. I suspect the 3 port valve micro switch or something like that.
Fixed it!, it was the stat on the hot water cylinder, happened to have a spare one in the loft.

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