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No HW -CH ok - suspect 3 way valve?

Postby Barnjet » Fri Aug 17, 2007 11:45 am

Some advice please. I have a standard Y plan vented system with a Honeywell V4073A mid position valve, ST 6450 programmer, L641A cylinder stat. There is no room stat - radiators temps are controlled by TRVs and the return stat on the boiler.

The symptons are:

HW only selected - the cylinder stat fires the boiler and the pump, but hot water only flows in the CH circuit.

CH only selected - the boiler fires and the pump runs with hot water to CH only. Rotating the cyl stat has no effect ( as expected)

HW & CH selected - same as above - hot water in CH circuit only.

Electrically, the following coloured wires are live/dead on the 3-way valve

HW only = White - live; Blue - dead; Grey - dead; Orange - live

CH only = White - live; Blue - dead; Grey - live; Orange - live

HW & CH off but Programmer on = White - dead; Blue - dead; Grey - live; Orange - live

Now, I understand from Honeywell

that in HW only, the [i]valve is not energised[/i], so why does it feel warm to the touch all the time, irrespective of whether the boiler is firing or not.

From some paperwork I have, I can tell that at some point, the original mid postion valve had a replacement motor head fitted and the installer has left the following notes on the installation sheet:
Blue - 1; White - 2?; Grey - 4; Orange - 5 (the question mark by the white wire is possibly a concern)

At this moment, I cannot tell whether this is a system wiring fault or a fault with the 3 way valve.

Any diagnostic advice welcome.
Thanks, Barnjet
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Simply Build It

Postby Barnjet » Sat Aug 18, 2007 1:29 pm

Success - after isolating the power to the 3 way valve, I removed the powerhead cover to see if the syncron motor moved when I selected CH or HW. It did not.

I then removed the powerhead itself and I "encouraged" the motor to work by inserting a large flat bladed screwdriver into the slot where the valve spindle would fit. With power back on, the motor cycled to different postions depending on CH or HW selection. In CH, the motor is electrically held against a spring which is biased to the HW only postion.

With the powerhead removed, I also gently twiddled the valve spindle, it only has a very short range of movement - about 10 - 15 degrees.

The system is now back on line and I can only conclude that the motor and/or valve were stuck through lack of use over a prolonged period of time. I have photos of the various stages but am unable to post them to this reply.
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