radiators getting hot when system off

[wildcat phil]

Hi guys...newbie here...I have a problem with our Vokera Linea 28 combi boiler, which is about 11 years old.
I first noticed the problem a few weeks ago when I discovered that the radiators were getting hot when just the hot water was running, even though the CH thermostat was on minimum i.e. 10 degrees.
A friend recommended a plumber, and after speaking with both him and Vokera, it was thought that the problem was likely to be the diaphragm in the diverter valve, so he got a new one and replaced it. It seemed as though this initially cured the problem, (although I cannot be certain that it did), but the problem has now returned again. He came back again on Friday and changed the diaphragm again, supposedly tested the system and left, but I immediately checked it and found the problem to be still present, so he came straight back and seems to think that the diverter valve itself is likely the cause of the problem. However, I came home from work at 7am on Saturday morning to find that our bedroom radiator (and possibly others too, although I didn't check any others) was hot, even though the thermostat was again on minimum, and no hot water had been run since the previous evening !! How can this be ????

 

[jackthom]

If Domestic Hot Water preheat is enabled (Boiler in Autumn or Winter Mode) the boiler will fire up occasionally by itself to keep the reservoir of water in the boiler hot. This is to try and avoid a long delay before hot water arrives when the hot tap is turned on.

The divertor valve is still the prime suspect.

 

[wildcat phil]

Cheers Jackthom...the boiler has always fired up on it's own for a short period, even in summer, but only for a few seconds, and the radiators were more hot than warm, so I am guessing that the boiler had been on for some considerable time, which is not normal. I can only guess that the diverter valve has stuck partly open, and is allowing this pre-heated water into the heating system too ?. The plumber did phone me back yesterday, just after I had posted this on here, and confirmed that his guys had put a new service kit in the diverter valve, but having read other threads about this issue, I am wondering if they haven't fitted it correctly, if that is possible ??
He also said that he was going to ring the Vokera helpline to discuss it with them, but I am still waiting for him to get back to me.

 

[wildcat phil]

Further development...I turned the room stat down to minimum (10 degrees) at 9.00 pm last night, as I normally do, but at around 10.30 heard the boiler fire up and continue to run and heat the radiators up. I then went to the control panel and switched that to off, so that the rads wouldn't get hot overnight, but woke up at 02.20 this morning when the room was stifling hot, along with the rest of the house !!!!!
The only thing I can think of is that the pre-heat is staying on way too long (for whatever reason), and that the diverter valve has stuck and is putting hot water down the rads ??

 

[Agile]

I would usually replace the entire diverter valve rather than use a service kit.

The difference being that a brand new part is back to the factory condition.

I have used the kits before and they take a while to fit properly and even so the internal parts can still leak.

Tony

 

[jackthom]

Further development...I turned the room stat down to minimum (10 degrees) at 9.00 pm last night, as I normally do, but at around 10.30 heard the boiler fire up and continue to run and heat the radiators up. I then went to the control panel and switched that to off, so that the rads wouldn't get hot overnight, but woke up at 02.20 this morning when the room was stifling hot, along with the rest of the house !!!!!
The only thing I can think of is that the pre-heat is staying on way too long (for whatever reason), and that the diverter valve has stuck and is putting hot water down the rads ??

With the divertor valve stuck, the water it's preheating is also going through the radiators and so it will continue until the entire system, boiler plus radiators, gets up to temperature.

I thought preheat could be turned off. Otherwise you may need to turn the boiler off overnight until you can get it fixed.

 

[wildcat phil]

Cheers guys...original plumber been back to me...he has spoken with Vokera who say that the pre-heat function can be disabled by removing a "jumper on the PCB" (???), but although that will stop everything getting hot when the system is switched off, it still won't cure the issue with the diverter valve evidently being stuck/sticking. I have just looked at the service book that they filled in about 4 weeks ago, and it only mentions replacing the diaphragm on the valve and not actually fitting a new service kit, so I am actually wondering if they even stripped it down ????
Unfortunately the original plumber is snowed under with work, so I have spoken with another plumber who is getting a service kit for the diverter valve and coming round later today to fit it...fingers crossed.

 

[wildcat phil]

Problem solved...plumber 2 has just left having stripped down and replaced the innards from the diverter valve. I would post a pic, but can't work out how to...suffice to say that they are filthy black, and are obviously the original factory-fitted items from around 11 years ago !!!!!!
I showed him the diaphragm that plumber 1 had changed and he said that was just the diaphragm from the flow switch, and he couldn't understand why they would change that, with the problem I was having !!!