Another heating wont turn off question

Hi,

My heating has developed a problem where it wont turn off while there is de= mand for hot water.

The hot water is timed to come on from 6am to 9am, ready for the morning sh= owers. The heating is also timed to come on durring that time with the the= rmostat in the living room controlling the demand. On the odd occasion whe= n the heating has come on in the morning (normally my daughter with the pat= io door open, complaining that its cold!!), it wont turn off until the hot = water has switched off. If I turn override the hot water timer, turn the h= eating thermostat downa nd turn the hot water timer back on, it works OK.

Its a standard Y plan setup.

Any pointers as to where the problem may be before I get started (I think i= t might be the 3 port valve motor).

Thanks

Alan

demand for hot water.

showers. The heating is also timed to come on durring that time with the thermostat in the living room controlling the demand. On the odd occasion when the heating has come on in the morning (normally my daughter with the patio door open, complaining that its cold!!), it wont turn off until the hot water has switched off. If I turn override the hot water timer, turn the heating thermostat downa nd turn the hot water timer back on, it works OK.

might be the 3 port valve motor).

I don't think it's the motor. The valve has 3 positions - HW-only (unpowered), HW+CH (mid-position), and CH-only (full travel). The motor moves the valve from the HW-only to the other positions, and a spring returns it when power is removed. If the motor fails, you're likely to get HW-only but *not* CH when there's no demand for it.

The innards of a 3-port valve actuator are quite complicated, with a couple of micro-switches, and a diode to hold the valve in the mid-position with the motor stalled. I'd put my money on the switches or the cams which operate them. There's an outside chance that the 'wet' part of the valve could be sticking, but mucking about with the demands wouldn't fix that - so that's not very likely.

When one of these valves gets its knickers in a twist, it sometimes helps to power it off completely (at the FCU which powers the whole system, not just at the programmer). This resets it, and it sometimes works ok after that.

If that doesn't work, and if you're satisfied that the wet part of the valve is ok (spindle turns fairly freely with actuator removed) I would suggest replacing the whole actuator - unless you fancy fiddling with micro-switches, cams and springs which fly in all directions.