3 port mid valve

6 May 2008
Reaction score
United Kingdom
i have no hotwater on y plan. programmer fine , cylinder stat ok , orange wire from m/valve dead? could anyone tell me whats wrong here. i thought m/valve electrics not used here as valve de energised open to port b? and boiler fired up by cylinder stat? many thanks
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programmer live to cylinder stat which then feeds live to boiler/pump.

have you live going in and out of cyl stat ?
so in hot water mode it doesnt matter if orange wire is dead because the valve is by default open to port b?cylinder stat fine, orange wire dead for both ch and hw
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You are correct in saying that HW only does not go via the MV. It is a direct connection from the timer HW ON terminal to the cylinder stat common.

The orange wire and the HW stat call wire usually go to the same terminal, so it is difficult to tell which one is actually live
. Disconnect the orange wire and check the voltage on the white and grey wires.

If the white only read 240V, then the valve is in mid position. The orange should read 0V
If both grey and white read 240v, the valve is in the CH only position. The orange should then read 240v.

If just the grey wire reads 240v, the valve is probably stuck in CH position.

Try turning off the power completely; this will allow the valve to reset.

Read Mid-position valve working and Diagnostics for more information.

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