Boiler venting into header tank?

[Alan60]

I have a 27 year old Baxi Solo and open vent which keeps venting hot water into the header tank. I have replaced the pump. The zone valves are working fine. I also have a bypass valve fitted. I have power flushed the system and also flushed with mains water. The system has always had inhibitor and I have used cleaners fairly regularly in the past. The water is clear when I drain the system. When the boiler is on all the radiators get hot as does the hot water circuit so it doesn't seem like I have a blockage anywhere. But after about half an hour the boiler makes a hell of a racket and it pours hot water through the vent pipe into my header tank. I am thinking of buying a new system boiler and going unvented but could it be anything else before I go to that expense?

 

[JCplumb]

Are you sure the pump is on the right way round? It should be after the vent pipe and pumping away from it.

 

[Alan60]

Yeah I have a Grundphos Alpha which I have just replaced and this seems to be pumping hot water around the system correctly as the pipe after it gets very hot with the return pipe being cooler. It is definitely situated after the feed and vent pipes. Someone suggested it could be the thermocouple?

 

[JCplumb]

Don't know about thermocouples, I know what one is but I'm not gas reg and only a gas reg guy should be checking it.
There are a few reasons why a system will pump over.
It's pretty much guaranteed to pump over if the pump is on the wrong way.
Also you mentioned a bypass, if that's fully open it could cause pumping over, if it's a lockshield/gate valve type, as long as you have open rads - try temporarily closing it to test, remember the position it was in though and put it back there after testing.
If it's an auto bypass what setting is it on?

 

[Dotty]

Do not take the case off the boiler.

You are not competent to do so. And forget the thermocouple, it most definitely isn't that.

Whomever suggested that to you needs their arse kicked.

 

[joni os]

Croppie has shown unusual restraint in not closing this thread. If model is solo RS, the one with a pilot light.,simplicity of design may warrant attention rather than replacement. The only repair worth doing is to descale the boiler and hope that in so doing leaks do not appear.
Figures, from energy saving trust, indicate a new efficient boiler would save between £215 - £350 per year at march 2016 fuel prices.

 

[Dotty]

And now I'm closing the thread.