BOILER BOILING

[simonadams]

I have a Glowworm fuel saver F100. I don't know how old it is as it was in when I moved into the house 5 years ago.
The system was working fine until I moved two radiators in the bathroom and the system was empty for about 2 weeks. I have filled it back up again and bled all the radiators.
When I turn the system on whether it be for hot water of central heating, the boiler fires up as normal and then after about 15 minutes it boils water into the expansion tank, and does not cut out.
I have done the following,
1. Stiped the boiler and cleaned the burners,
2. Cleaned the outside of the heat exchangers. There was a large build up of some kind of hard material, any ideas what this could be ??
3. I found that at some point the over heat stat had been by passed to the main stat, and so as a precaution I replaced the overheat stat.
4. I have replaced the pump.
5.have tried turning the main stat down, but when it below '2' the boiler does not come on at all.

When I tried it again, it worked for about 15 minutes, it started to boil and then cut out. It would not restart again, so I bypassed the over heat stat and it worked until it boiled again, so I had to manually shut it off.

I am getting married very soon and could do with it working !!!

Any ideas would be much appreciated.

 

[croydoncorgi]

From your description, the boiler is working but overheating because there's no circulation of water through it. That it does not cut out once it has overheated is worrying. you also say that you replaced the overheat stat - does it STILL keep going even with the new stat? Probably there's some air left in the system which is preventing water from getting round.
Is the pump running silently or with a lot of air-noise? Have you checked for air-vents on / near the HW cylinder plumbing? Have you loosened the central screw on the end of the pump casting to vent the pump?

 

[simonadams]

I think there is water circulating through the boiler as it does warm the central heating and hw but it does boil over.
i replaced he new stat which did cut the boiler off at the point of it boilingg but from then on the boiler would not relit even when stone cold, this is when I by passed the overheat stat and then it relit, but of course boiled again.
I have bled the pump and no air was present. The system is quiet for about 10 minutes and then the water can be heard running through it after another few minutes it boils.
One thing I forgot to mention was that once it has boiled and I manually shut it of there is a significant sound of water running back into the boiler.
I have not yet checked the vent on the boiler. I will do it now and let you know,

thanks in anticipation.

 

[simonadams]

I have tried the vent near to the cylinder, a very small amount of air came out but hardly any.

anymore ideas ?