Boiler kettling…advice please!

[FrankHarrington]

Hi guys,

This is my first post and I'm only recently qualified so... A customer called me to look at their boiler because it is kettling. It is a Potterton kingfisher MF on an s-plan vented system. It is a semi-pumped system, the hw is gravity circulated and ch pumped. It happens intermittently and not until the systems been on for an hour or two. It then starts banging loudly and spitting out the open vent, consequently the overflow also. They had an insurance cover on their ch (don't think bg it was another) and they sent a couple of engineers out who replaced the pump, checked the boiler stat (apparently) and suggested the feed pipe was blocked or the system needs flushing. Im reluctant to carry out an expensive power flush as the system heats up normally, there are no cold rads and the hw works fine. I don't know if its a red herring but the boiler stat sometimes cuts in and out rapidly, although like i said they apparently checked the stat.
Any help much appreciated!!

Frank
Harringtons Heating and Plumbing

 

[chris watkins]

I think your heading in the right direction Frank, what could be causing the system to over heat to such a degree that the water in it boils ? because that is what is happening for the water to come out of the open vent when the system is getting up to temperature.
Could it be the C/F blocked ? well if water is being lost out of the O/F then how has the system still got water in it ?
With the other stuff all of which are flow related, you would be looking at how the system was/is heating up, with the gravity side this should tick away with out a problem as a pump is not required, so any restrictions to the flow would cause a rapid rise in the temperature.
So what do you recon it is ?
Welcome to the mad house (forum) by the way.

 

[jtsplumbing]

Are you in a hard water area ??

 

[stevetheplumber]

Are you in a hard water area ??

your not going to suggest that a cast iron boiler is scaled up?

 

[dancinplumba]

your not going to suggest that a cast iron boiler is scaled up?

oh no heisn't

 

[FrankHarrington]

I have checked the c/f isn't blocked by draining the system to check that the f+e tank emptied which it did normally. I can't see how there can be restrictions in the system as i can feel the heat moving round fine. I have a hunch that it is the thermostat, as theyre relatively cheap I think I'll stick a new one in and see where it gets me. Do you guys think thats a possible cause?

 

[FrankHarrington]

And you obviously don't think its the heat exchanger being scaled up? As that was a possibility I had drawn from reading other threads on here :confused5:

 

[chris watkins]

Sorry Frank I though you had got to that point after your / my first posts ? I should have not been so cryptic. I can't see that it could be any thing else.

 

[FrankHarrington]

Nice one Chris thanks for the quick reply I will let you know how I get on!