Central heating: lost pressure

[harrypotter]

Yesterday I bled one of the radiators. I didn't realise but apparentl

you're not supposed to do it when the heating is on. So, now I've los pressure in the system.

I've been told that to fix it, I need to find the pressure tap an raise the pressure to 1.5 - I've looked all over; there's no tap and n gauge.

Maybe I've got an old boiler - can anyone suggest where these might b

(no where near the boiler - really, I've looked everywhere)

Ta

-- harrypotter

[gastec]

what type of boiler do you have???? Gas Council number ?

-- gastec

[harrypotter]

The make is a Potterton Netaheat Electronic

I don't know about the gas council no - where would that be written

-- harrypotter

[gastec]

The old potterton netaheats are usually not pressurised and therfo there is no fillup loop or pressure gauge...

I bet that you have no water in your small header tank in the loft or choked cold fee

-- gastec

[harrypotter]

right..I'll get the ladder.

thanks,

:

-- harrypotter

[Richard Conway]

How do you know you've lost pressure?

[harrypotter]

Ah...good point. I just assumed that because all the air has come ou

of the radiator (I could hear it) and then no water followed, it mean that there's no pressure left

-- harrypotter

[Rob Morley]

There should have been water - have you got thermostatic valves?

[Richard Conway]

You should try opening the bleed screw on another radiator and seeing if you get water from that. Do the radiators get hot when the system is on?

[harrypotter]

no, the boiler fires up for 3 or 4 minutes and then stops - none of th

radiators heat up. by the way, I tried to bleed the pump as well thi afternoon; no water came out of that either

-- harrypotter

[Set Square]

Someone asked earlier whether you had checked the fill & expansion tank. I don't recall seeing an answer.

Assuming you have got a vented system (rather than a sealed/pressurised system) you should have two tanks in the attic - a large cold water header tank for the hot water system, and a small F&E tank for the primary circuit. The chances are that this small tank has run dry because it's ball valve has stuck shut. Make sure it's got several inches of water in the bottom - enough to cover the pipe which feeds the heating system. If it's empty, sort it out and re-bleed everything.

If it *has* got water in, it's possible that there's a tap or gate valve in the pipe between the bottom on this tank and the heating system - and that the tap is closed. If this is the case, open the tap (and *leave* it open) and re-bleed everything.

[Richard Conway]

Have you worked out if it is a pressurised system or one with a small header tank in the loft yet?

[Ed Sirett]

Agreed. The boiler fires for 3 or 4 minutes is a classic no flow (no water/ bust pump) symptom on older systems. With a Netaheat it will be nigh on certain this is an open vented system.