I’ve a central heating/Hot water problem - basically heating works fine, but when heating is on it also heats hot water and visa versa. After a bit of diagnosis I am sure the fault is the Honeywell 3 port V4073A motorised valve.
I’ve removed the motorised section of the valve and the motor appears to be stuck. As the valve section moves I was planning to replace motor section, however before I do I wanted to check how much the valve should be able to move.
My valve is easy to turn by by hand but moves only about 45 degrees - is that normal? If so it’s a motorised head replacement which I can do - if not looks like I’ll need a plumber to replace the whole valve.
There are two wires controlling the valve, white and grey, white is live to get central heating and grey is made live to turn [u]off[/u] domestic hot water, so with the head removed from base you should get domestic hot water only.
Also the valve turns on the central heating, the Orange wire fires up the boiler and pump, so set to central heating only, if the valve is stuck, then central heating will not work.
One thing which happens is the micro switch fails, either stuck on, or stuck off, one work around when stuck off is to manually latch the valve which opens valve half way giving both central heating and domestic hot water, do ensure it's not latched.
When you move the leaver with no power you can feel resistance from the return spring, it it has motored open then no resistance felt, so you can detect if open for central heating.
So it does not move to give domestic hot water (no power white power or grey), it moves half way to give domestic hot water and central heating (power white no power grey), and it moves all the way to give central heating only (power white and grey), however the cylinder thermostat powers the Orange wire direct when domestic hot water is required.
So with a faulty motorised valve head you may well get domestic hot water with central heating on, but you should never get central heating with only the hot water turned on as the valve is not powered for domestic hot water only.
However the micro switches are not as simple as diagrams show, so it may be possible with some valves for the Orange wire to back feed valve, Orange is an output not input so should not cause the valve to move.
So it you temp remove the Orange wire, put it in a chock block, working dead of course, then domestic hot water should still work, but no central heating, and valve should not move. Since you get central heating the valve must have motored.
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