Replaced 3-way valve but hot water still heating radiators.

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We recently moved to a house with a conventional heating system, with a digital wall thermostat and Danfoss 4033 boiler controls - the classic red and blue tappets!

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The heating is always switched to ON on the Danfoss, with the wall thermostat deciding whether it is on or off, and the water is timed. But when the water comes on, so do the radiators, even when the wall stat isn't calling for heat. I reasoned that the 3-way valve was the problem and so did the British Gas engineer who came out to fix it. But replacing the valve hasn't fixed the issue.

If I switch the heating to OFF on the Danfoss box while they are being unnecessarily heated, the radiators go off. I can hear the valve closing when I do it. Could the problem be incorrect wiring of the heating controls? I want to replace the primitive Danfoss controls because I don't need an tankful of hot water heating every evening, but I don't want to introduce new equipment to a faulty system if I can avoid it.

Any help much appreciated.
 
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Reverse circulation.

That was my first thought as well, but being a hydraulic problem I wouldn't have thought it would resolve itself when the heating was turned off at the timer.

So although I am stumped as to the true cause I would certainly be checking the wiring carefully, particularly that the room stat is interrupting CH_ON properly.

Op, if you have a multimeter and know how to use it, you could check against a standard y-plan diagram (Google) bearing in mind that the wiring may have been slightly modified, to suit pump overrun etc.
 
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Thank you for the responses! I figured that reverse circulation might lead to a couple of radiators coming on but surely not every radiator in the house being on full when the water tank is heating up - which is what is happening. I'll get a electrician out to look at the wiring; beyond fitting a light switch or a thermostat, I know my limits.
 
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Have you got the valve the right way round ? Port B going to cylinder coil ?
 
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