Another heating wont turn off question

On 24/07/2012 15:46, AlanC wrote:

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.
--
Cheers,
Roger
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