Ask The Trades - Print Page

Ask The Trades
https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Plumbing Questions >> Grant open fire back boiler https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1325754931 Message started by maldevlin on Jan 5^th, 2012, 9:15am

Title: Grant open fire back boiler
Post by maldevlin on Jan 5^th, 2012, 9:15am

Hi there,
I recently moved into a house with an open fire and a grant back burner.
I have noticed a problem and have managed to pinpoint this down.
When I light a fire the boiler does it job and it heats the cylinder and then in turn the pump come comes on and dumps the water to the rads however ive noticed that when the fire is burning a long time (say 4hrs) that I start to hear the cylinder making banging noises (might be pump) and i note the pump stops pumping and the whole things gets hot, this is ok but then this same pump wont work when you switch on the oil burner. So in a cold night then nothing is heating the rads. generally when the hot water in the tank cools off or is dumped i find the oil boiler starts to work again and the pump works as normal. Now if i dont light a fire the pump and the oil central heating works perfectly without problem so I am assuming that the pump is not liking the heat of the water produced by the back burner at the fire, the stat on the cylinder (that controls the pump) is set to 45d and ive been told that seems fine, the stat must be working ok if the back boiler works fine for the first few hours etc.
Its an odd one and im thinking the open fire/ back burner while nice is too much hassle.
It wouldnt be so bad if it didnt stop the oil boiler using that same pump thus leaving me without heating for 1/2 day.
Any help would be appreciated...

Title: Re: Grant open fire back boiler
Post by thescruff on Jan 5^th, 2012, 10:26am

There's too many like this that has been chucked in by DIYers and potentially very dangerous.

Get it check over by someone that knows what they are doing.

The Cylinder shouldn't boil.

The oil boiler should have it's own pump.

Title: Re: Grant open fire back boiler
Post by CWatters on Jan 5^th, 2012, 11:59am

What he said, get it checked. Steam explosions are very dangerous - not just because the explosion is violent but because when steam condenses it gives up a lot of heat without cooling down (google latent heat of condensation). Makes it much more dangerous than water at 100C.

I believe systems like this are normally designed to fail safe in the event of a power cut so I think they are usually gravity fed rather than pumped. Also common to have a heat dump rad to dissipate excess heat when the tank is upto temperature to stop it boiling. Sounds like that's not working right and could be pretty dangerous.

Title: Re: Grant open fire back boiler
Post by maldevlin on Jan 5^th, 2012, 12:57pm

thanks a lot, actually i forgot to say that there is a pump also at the boiler but when the fire causes the whole thing to overheat (i say overheat but im not sure) then the boiler cuts out after 10 mins as the pump at the cylyinder has stopped working & therefore i dont get heat to the RADS, if i leave it overnight then it seems to all work ok again, the previous owner said he used to fill bath to dump water then all corrected itself. It seems that the 2nd pump at the cylinder is overheating (ive replaced it and no help) and im wondering is it possible the stat is faulty or maybe even just needs set to a lower setting? its a tricky one and im wondering if the back boilers are worth the additional complications

Title: Re: Grant open fire back boiler
Post by thescruff on Jan 5^th, 2012, 1:18pm

The cylinder stat may be cutting the boiler/pump off wrongly.

It really needs checking over properly before you use the back boiler.

Title: Re: Grant open fire back boiler
Post by maldevlin on Jan 6^th, 2012, 4:04pm

it would appear i have solved the issue, the stat was on the wrong pipe!, it wasnt on the back boiler pipes at all so by the time the wrong pipe was warm enought to engage the stat then pipes from the fire were at melting point!!
it looks like the stat has been on the wrong place for the last 18yrs since the house was built!
....
thanks all..

Title: Re: Grant open fire back boiler
Post by CWatters on Jan 7^th, 2012, 5:14pm

I'd still get it checked. Not obvious why the back boiler needs a pipe stat.

Title: Re: Grant open fire back boiler
Post by thescruff on Jan 7^th, 2012, 5:38pm

CWatters wrote on Jan 7^th, 2012, 5:14pm:

I'd still get it checked. Not obvious why the back boiler needs a pipe stat.

To bring the heating pump on CW

Title: Re: Grant open fire back boiler
Post by CWatters on Jan 7^th, 2012, 10:55pm

Are you allowed to pump a soild fuel boiler? I thought they had to be gravity. I'm probably wrong or I've missunderstood his system.

Title: Re: Grant open fire back boiler
Post by Lectrician on Jan 8^th, 2012, 10:43am

I gather the cylinder is heated through gravity from the back boiler, the pump being on the CH pipework, taking heat from the tank, which has been independently heated by the back boiler.

As soon as the pipework gets hot, the pump to heat the rads comes on.