The problem is that if the 3 port mid-position valve is on ‘Water’, when the room thermostat then calls for heat the valve does not move across to the mid-point or 'Heat'. If I move it to Heat using the manual override on the mid-position valve, the heating then clicks on immediately and works normally (... until water is next needed and the valve moves to “W” & doesn’t move back).
A couple of facts: - The room thermostat is a 4 year old Honeywell CM907 (ie a fairly sophisticated digital one). - The mid-position valve is a 10 year old British Gas model. It’s generally in poor condition, with a couple of bits of plastic that have come off. - The time clock is maybe 20 years old. I leave the CH switched to ‘On’ permanently and use the room thermostat to control it. - My impression is that the wiring is generally ‘antique’. - I’m want to replace the whole set-up & boiler in the spring.
My thinking is that the mid-position valve is the most likely suspect. Anything I’ve missed out before I shell out £70?