Two weeks ago heating stopped working - but hot water production still OK. For a few days following, if I moved the toggle lever on the Honeywell V4073A motorised valve from Auto to Manual it would fire up the boiler sufficient to get the rads warm - but then it would stop. I also noticed that the body/casing of said divert valve was incredibly hot ! Way too hot to touch. The valve is fitted snug up to the side of the cylinder (foam insulated) and I also have plenty of additional lagging around cylinder - including over the divert valve...so initially I thought this was the cause of high temp of outer casing.
So I bought a new Honeywell valve. Yesterday, I replaced just the motor part of the valve (not the 3 port brass and ball part) and everything returned to normal. System now correctly responds to all demands - hot water and rads all as normal. Room stat and clock all working correctly too. But....the outer casing of the new circular motor is, once again, unbelievably hot - way too hot to touch. Seems like the circular motor is running flat out the whole time - even when the boiler has not been on for hours. Is it in the process of burning up, like the previous one ?
Any ideas ?
One other clue (maybe)...when I had the old valve assembly off I manually moved the spigot shaft of the ball from side 'A' to side 'B' and back again, many times. It moves freely - spigot didn't seem stiff. When the pump was running the ball valve goes over with a thump in the pipes - as though the ball was making a good seal across the flow.
Many thanks for ideas.