Hello. I have a similar system to that mentioned above. Since the weather turned colder a couple of weeks ago we have been unable to have heating without the hot water being on. Once the hot water reaches the desired temperature, the boiler shuts off and the only way to get heating again is to use the hot water up. I already had a spare programmer originally changed for visual reasons which I swapped back but no change. I have rung approximately 15 local plumbers and all seem too busy to come out! Full spec is as follows:

Potterton Promax 24 HE
Heatae Sadia Megaflow

Pictures attached!

Any pointers would be appreciated.

TBM, November 2009

It was the motorised 2 way valve. The manual overide lever had bent so wasn't activating hwen pulled across due to it being made of monkey metal! I removed the pressure spring from the lever and pulled it across with a screwdriver - hey presto - central heating!!!! Off with the wooly jumpers! New valve is on it's way.

TBM, November 2009

The valve doesn't appear to be doing anything even when I manually move the lever across. It's a Honeywell 272848 2 way motorised valve. What's the best way to test it, i.e. what wires do I put my meter on?

TBM, November 2009

sounds like possible motorised valve for heating not making the end switch to send power to the boiler. so by drawing hot water you make the boiler fire (to reheat the cyl) and the valve for heating is probably opening but just not quite enough to hit microswitch alone so you need the power from the h/w mv to get it to fire. prove it first with multimeter as any good diagnosis, then replace motorised valve head if found faulty.

ste, November 2009