Ravenheat RSF100ET

My Ravenheat RSF100ET is some 7 years old and has had various problems but the latest one has troubled my limited skills. Recently it has started heating the radiators whilst hot water is in use, and I know that is either the 3 way valve or the DHW pressure switch. But now even with the timer off, and the main switch on DHW only, the heating is staying on all the time. Resetting the mains switch or even power cycling the supply does not stop the heating. After leaving the supply off for longer period, it seems to be okay, until it starts the heating yet again! I can't work out what would run the heating all the time.

 

....

 

It's a combi so wont have a 2 port.

 

Op you may be better off posting this in the plumbing forum ??

that Ravenheat is a a lot older that 7 years , as in 2005 all boilers had to be condensers / steamers/ high efficiency boilers . that model is a standard efficiency boiler / combi

the term 3 way valve will cause confusion as its a combi the correct term would be a divertor valve. afai recall its a gianonni type divertor valve ?? may be ? possibly ??


edit
AJ beat me to it

 

I was only going on the three-way valve.

Second time today I shouldn't have believed posters.

 

It's almost like real life

 

I beg your pardon, it is a diverter valve. It was bought just when the new rules were coming so must be 2005. Today, as soon as power to the boiler is switched on, with main switch set to DHW only, and with both thermostats set to minimum, the heating came on and I couldn't get it to go off. Now worried about having a serious accident with it!

 

If your that worried then call someone out to look @ it.

 

The diverter valve was playing up, replacement did the trick! However now I have new intermittent issues. Whether on Heat or Hot water, the Fan and motor run fine but doesn't always fire. After a couple of more tries it still may or may not fire. If it doesn't the red light comes on. After resetting, again same situation. Sometimes it will work fine for a couple of days, at other times after resetting some 20 times, it will suddenly work ok. I don't hear it firing either. Relay 3 just will not operate. Very occasionally it will fire and light for a split second, then fail again. I've replaced both thermistors and I've checked the air-pressure switch by blowing into the pipe that goes into the flue and it works fine. Got a second hand tested board this morning, but same issues persist so I assume board is fine. Is there any way of checking the gas switch and the electrode cables? Any other suggestions are most welcome!