Gravity Fed Boiler Problem - Please help!

[JimboGog1]

Thanks for reading my post.

My central heating system has developed a problem and I need some guidance if I may, as follows:

I have a gravity fed gas boiler with four 1 inch feed pipes. Two which feed the radiators and two which feed the hot water system. Although old, the boiler has worked fine up until now...

Now however, every time the pump winds down it sends a surge of boiling water from what appears to be the boiler all the way through the hot water pipe, through the hot water cylinder (located in bathroom) and then up to the expansion tank in the attic. When this happens, the pipes make an almighty racket and physically contract under the pressure/ heat. This last for a few seconds every time the pump switches itself off

One second you can have your hand on the hot water feed pipe and the next second it is literally too hot to touch and then cools down almost as instantly – making some very laud scraping, moaning, banging noises.

I have been up to the attic and the expansion tank, although not overflowing is very hot.

Does anyone have any ideas what is happening before I call a plumber?

If you need any more information please let me know.

Cheers

 

[namsag]

Have the radiators been really hot to the touch and water coming out taps a lot hotter recently

 

[crashndie]

sounds like the boiler stat is broken or set to hi. has anyone turned the pump speed up?

 

[JimboGog1]

No the radiators seem to be all the same temperature so no change there and even the hot water seems to be constant...?

No one has touched the pump speed as far as i know - it is set to three though, is that ok?

 

[JimboGog1]

p.s. what would be causing the water to shoot round the system when the pump goes off, at times it sounds like the whole system is going to explode (new to all this so sorry for my ignorance)??

 

[Biguns]

What boiler have you got ?

 

[JimboGog1]

It's an old ferroli one - not sure which model though.

 

[Biguns]

I had this problem with my 20 year old Thorn Apollo. Turned out to be the pump overrun stat, which ensures the pump runs on for a few minutes after the boiler has shut off, this to get rid of the residual heat in the boiler.My pump was shutting down with the boiler and the residual heat caused the water to boil and take the shortest route to the FE tank with all the accompanying accoustics and hammering
Im not certain, but I dont see why your system won't also have a pump overrun stat. Worth checking

 

[Biguns]

If you can get your model type/No you can go to the Feroli site and download the manual for it