Plumbing and Central Heating

[PaulWH]

Y-plan installation. Honeywell Sundial Plan Wiring Centre installed. Honeywell V4073 Mid-Position Valve used.

Issue:- With programmer set for CH only and with no demand from Room thermostat sometimes the Boiler remains running.

I have read that the boiler/pump gets its power from the hot water tank thermostat when a hot water, or shared demand is made.

Does this mean that the Boiler will stay on until the hot water tank temperature is up to temperature before turning off, even though there is no demand for HW and the CH side of things is satisfied? I ask because if I manually turn down the set point on the hot water tank thermostate the boiler will turn off and if set higher again, will turn back on.

At these times I have 240V on the grey, white and of course orange cores on the mid-position valve, is this correct?

Would appreciate any comments because if true then it means I cannot run CH independantly from the HW circuit if the hot water tank temperature is not up to temperature.

Thanks

PaulWH

 

[D_Hailsham]

If the CH is off at timer or stat, the Boiler is controlled directly through the HW thermostat. The 3-port valve is not energised.

This link will take you to the Sundial Wiring Centre Instruction Sheet

This link explains How a Mid position Valve Works

Here is the wiring diagram for a Y-plan. It does not use a sundial wiring centre, but is easier to understand.