Two radiators not working

Dear All,

a plumbing newbie and useless person here.

Story is this, had a loft conversion done, which needed the header tank moved and 2 new rads installed and one moved.

previoulsy the system work very well. It is an old thorn bolier.

However, the new radiators would not heat up, have had the plumbers back many times with the following effects

1 Your pump in not man enough - therefore father in law and I upgraded pump no joy
2 you need a new boiler - ignored this one
3 they turned up and got them working
4 the rads went cold the next day. When bled no air or water came out at all, you could leave the vent open,
5 All other rads are not as hot as they were
6 The plumbers returned got it all working, but then it has failed again, One stays cold, the other is lukewarm and needs bleeding everyday and black water comes out.

The plumbers have been back 4 times with no joy, any tips please

thanks

Does header have water in it?
They won't work with air in them
Look at header when the pump on - any "pumping over"?

New rads/valves or old?
TRV Valve one end could be stuck shut
CLose lots of other rads - do they work then

If water is black @ top of rad when venting i would say you have a sludge problem which has also blocked your cold feed

Hi

They are new radiatiors installed by the plumbers,

When the plumbers were here last they checked the header tank and it was full, will check tonight and also mess around with the valves.

I recall that when the plumbers were back last they turned off all rads and could not get them to heat up. They managed somehow buit it has reverted back again.

thanks for your postings

mark

Is the header tank at least a foot above the top of the highest rad?
Have you checked for a blocked cold feed yet?

yep the header tank is about 4 ft above the last rad.

incidently the last rad is full, but never heats up
the 2nd rad needs bleeding constantly and warms up
all the other rads warm up but are no whey as hot as they used to be.

cant get the temp above 18c, used to have no problems.

will be phoning plumbers again tonight, if they state that I need a new boiler is this a possibility.

it is a Thorn and there are 10 rads.

cheers

yep the header tank is about 4 ft above the last rad.

incidently the last rad is full, but never heats up
the 2nd rad needs bleeding constantly and warms up
all the other rads warm up but are no whey as hot as they used to be.

cant get the temp above 18c, used to have no problems.

will be phoning plumbers again tonight, if they state that I need a new boiler is this a possibility.

it is a Thorn and there are 10 rads.

cheers