An old free standing boiler problem

[Deelta]

it is and old cavity system, no zone valves just a boiler, pump and controller for DHW & H/DHW, the problem on DHW only after few minuets start to make a knocking nose and a boiling water comes out of the vent pipe, any idea?

 

[charlieboy3]

it might be worth checking to see if the f&e tank has sufficient water in it, if this is ok i would suspect there is either a blockage in the cold feed or the boiler stat is not working correctly.

 

[Deelta]

it might be worth checking to see if the f&e tank has sufficient water in it, if this is ok i would suspect there is either a blockage in the cold feed or the boiler stat is not working correctly.

the feed tank is full, the cold feed !!why doesn't do that when the heating is on?

 

[charlieboy3]

do all the rads upstairs heat to the top? have you had the heating on long enough to get to full temp? is there a thermostatic valve in the return on the cylinder?

 

[Agile]

I think that you should be checking the pump !!!

It its too hot to handle then it is probably not turning! See FAQ.

Tony

 

[Deelta]

I think that you should be checking the pump !!!

It its too hot to handle then it is probably not turning! See FAQ.

Tony

the pump runs only on H and its off on DHW and that as you know the classical system, its not a fully pumped system

 

[charlieboy3]

I still think there is a blockage in the cyl primaries, or the temp regulator in the cyl return has stuck(provided you have one)

 

[Deelta]

I still think there is a blockage in the cyl primaries, or the temp regulator in the cyl return has stuck(provided you have one)

OK thanks I check that

 

[namsag]

Do you actually get hot water, if so the gravity flow and returns are not blocked . Noise etc sounds like the boiler stat has gone even if the gravity return was blocked the boiler stat should turn boiler off before it gets that hot it shoots water up open vent. If no hot water it could be a mixture of two faults

The reason is is not happening on the heating is because the extra pipework and rads and a pump running gets rid off the excess heat, if you left heating on for several hours without the roomstat turning off you would get same symptons with rads red hot to the touch

 

[corgiman]

the reason why the CH dont bang and crash is that the water level has not got down to a point where circulation through the rads is not possible

but it has for the hot water primaries

you have a blocked feed, trust me I am handsome

 

[Soggy_weetabix]

There could be an airlock in the Primaries. Are there any long horizontal pipework runs on them that could sag and collect air?

Could you not back fill the system as a tempory measure if the c/feed is blocked?

Chances are you may be able to clear it with 'compressed air' and some rubber tubing forced into the cold feed where it leaves the header tank.
I am in no way advising you of doing this if your not sure what your doing.

David

 

[Deelta]

I still think there is a blockage in the cyl primaries, or the temp regulator in the cyl return has stuck(provided you have one)

thanks it was the boiler's stat

 

[namsag]

Told ya so .

 

[Deelta]

Told ya so .

Thanks mate