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Radiators hot - central heating selected "Off" at

Postby NAROBS » Fri May 16, 2008 7:08 am

Fully-pumped vented system, Glowarm Fuelsaver MK II, Grundfoss pump, 4-litre pressure control sphere, HW indirect cylinder, Honeywell controls (Including 3 port motorised valve on boiler output) and Randall 24 hour electro-mechanical programmer. All equipment located in loft space. New-build installation 23 years ago.

With the central heating selected "Off" on the programmer, and HW on "Timed" radiators still hot. Turning down air thermostat to zero reduces radiator temperature to luke warm.

Is this just a motorised valve fault or M.V. + programmer error ?

I've already been up in the loft some months ago and used the valve manual slider to move the position - this seemed to do the trick for a while. Now the problem has returned.

Also, the system regularly vents water from the pressure release valve - it has done so from new. This occurs most frequently when the system is set to HW only. The pipe run from the boiler to the HW cylinder is very short, no more than a couple of metres.

Grateful for any advice.


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Simply Build It

Postby lisdar » Fri May 16, 2008 1:49 pm

Could be wiring fault to test remove head and put water on and cylinder stat set to high does the valve port to water only turn stat off does the valve port to off
Do the same with heating only testing room stat and clock to on then off
Does the valve port to off if all ok the wirings ok?

Most likely valve body passing some valves can be split what make and model is it
Remove inner body after shutting off isolation valves on pump, cylinder, and
Heating circuit
clean and re-assemble turn on isolation valves fill and vent pipes and away to go
If you need a new valve
buy ACL removal head and body for about £50.00 best on the market
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Postby NAROBS » Fri May 16, 2008 6:32 pm

Motorised valve is 3 port Honeywell sundial Y plan, mid-position, 22mm probably a V4073A. This is positioned on the flow side, directly after the pump, which itself sits on the flow pipe immediately after the point where the flow pipe emerges from the boiler. As you look at the front face of the valve, the port on the LHS is the CH flow to the house, the port on the RHS is the HW flow to the Cylinder and the port underneath the input flow from the pump and the boiler.

I suspect that when the programmer is set to timed HW only, that the valve is not closing or closing fully to seal off the CH outlet - hence warm rads - seems to be OK on constant - hence my original question extended to a possibe programmer fault.

This only seems to happen in when the programmer is set to HW only.

The actual outputs of the system are OK i.e. the rads are piping hot and the HW too, whenever they are selected. It just this minor technical issue that the rads seem to be heating-up when the CH is selcted "OFF" at the programmer.

Do you know what resting position of this valve is i.e. when it is not receiving or reacting to electrical input - should it be, as the name suggests, "Mid-position" ?


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