Big Air Blockage

Can someone please tell me what i need to do next

i have a potterton prima 50e gas heating
just replaced a faulty valve body. but now i have air in the system and my heating has lost interest
pump is working.
header tank is full.
but when heater kicks in 5-10secs later it spluts out hot water from the pipe above the header. heating then cuts out and the little black button on the bottom of the boiler pops out and i need to wait 5 mins for it to go back in.
i have vented the 2 air caps in the loft but nothing happening here(no hissing or water)

cakeman said:

but when heater kicks in 5-10secs

Click to expand...

What is a "heater", and what does "kicks in" mean?

faulty valve body.

Click to expand...

What where and how valve body?

sorry Softus - i mean when the boiler lights the pilot and ignites

sime10 - Valve body which is for the actuator to the radiators, old one was leeking from the spindle.

sorry about that guys , hope this is a little clearer
thanks for pointing out my bad use of words

If you draw off a pint of water from a drain cock, does a pint of water flow from the tank in the loft, followed by the float valve opening and it filling up again? If you have no assistant, fill the tank slightly above its normal water level and see if it drops.

I think you may have a blockage in the feed and expansion pipe. This is very common and prevents the system refilling after you have been working on it and drained some water, and leads to no water coming out when you try to vent the upstairs rads.

You often discover this after you have replaced a radiator or valve and the system doesn't refill.

It can also lead to insufficient water in the boiler, so boiling, overheating and so cutting out.

If this is the case do not try to fire the boiler again until it is fixed.

think you may have it John D

the header tank doesn't seem to have lost anything. i filled right up to the overflow by pushing the ballcock down (thinking the system may need a good drink) but none has gone

do you have any tips on fixing the blockage . it seemed to flow out when i took the valve body off , so can assume the blockage must be at the other end

It is very frequently on the Tee where the 15mm pipe from the loft joins the 22mm or 28mm circulating pipe. This will usually be close to the pump.

Usual thing is to cut out the tee (and its blockage), poke the ends of the pipes clear and re-join (use compression fittings as it is very difficult to get the pipes dry enough to solder). Then use a chemical cleaner; flush well, refill with inhibitor. If you can spare £100 extra fit a Magnaclean which will attract and retain the circulating black sediment and prevent it accumulating into another blockage later. Otherwise if you have used compression fittings it will be easy to dismantle next time.

Bale out the loft tank first or bung it. (when you cut the tee off all the water will gush over you).

If you seek novelty and excitement, hold a magnet next to the copper tee, as the blockage is from iron and will attract the magnet, unlike copper pipe.

It is sometimes possible to dislodge a blockage by (1) putting mains water pressure down the vent pipe (2) sucking on the vent pipe with an Aquvac but cutting it out is more certain.

Blocked cold feeds....what fun awaits you

The best one i went to was to rescue a colleague...the gate valve to shut the F&E off had dezincified and sheered off completely when he tried to close it, so he was stuck there with his thumb over the gaping hole in the fitting madly telephoning me to get my a** there as quick as possible and bung it in the false roof...oh how i laughed.

Alfredo

Thanks JonhD

1st - I syphoned as much dirty water and flushed the header tank a little
2nd - i chose to fasten a piece of garden hose on the piping directly below the pump at the bleed point, fastened with jubilee clip. Then i fastened the other end to the outside tap and slowly eased the tap open. After a few moments water began to flow up to the header tank.
then i repeated step 1 a few times.
i have now got the hot water to work and not wanting to be greedy and undo all my good (lucky) work so far i will do the heating tomorrow.