Airlock from hell

[Frampey]

Hi all, I have a fully pumped open vented system which I believe has a very stubborn airlock and I have run out of ideas.

The setup consists of a boiler which is a potterton profile 80e with a hot water cylinder, pump, 3 way valve, and f&e tank in the loft.

I had to drain the system down as I had a patchy radiator that was full of gunge. The radiator has been cleaned out, the system runned through several times, and radiator reinstalled. As a lot of work is being done in the house I removed most of the rads upstairs and left them off, just leaving two towel rails on. Downstairs rads are fed from a number of drops which are still on.

Since the draining I have filled from the feed tank, bled all the rads from downstairs up, bled the pump, and nipples adjacent to the hot water cylinder. I've also had the 3 way valve in manual to aid filling.

So when I fire up the boiler for HW demand, it runs for 5 minutes, makes the kettling noise, overheats and shuts down. The feed pipe is too hot to touch and return is considerably cooler, hence my airlock suspicions.

I've also backfilled the system through the flow drain valve adjacent to the boiler, and still no joy. Is the 3port valve position important when backfilling?

I've also considered adding a drain valve to the return pipe to the boiler to try back filling from here. Is there any value in that?

Any suggestions welcome, thanks!

 

[Crofton Gas]

Try isolating all the radiators, run pump on full speed, and vent from manual vent near cylinder

Regards

 

[Madrab]

I take it you mean the flow pipe, from the boiler? Were the valves on the boiler closed? Check the pump, if it was empty for a while it could have seized up.

 

[Terrywookfit]

I take it you mean the flow pipe, from the boiler? Were the valves on the boiler closed? Check the pump, if it was empty for a while it could have seized up.

An open vented boiler should have no iso valves.

 

[Madrab]

Oops .... typo.... should have been "were the valves on the pump closed"

cheers @Terrywookfit

 

[Frampey]

Thanks for the responses guys.

The pump seems to be running well, not instantly overheating, not making a horrific noise, bleeding nicely, warm pipes either side. Isolation valves either side of pump definitely open. I have tried switching back and forth between slow and fast on the pump too, no joy.

I have been venting from manual vent near cyclinder, I could probably bleed it for 2 seconds before water appears, every 5 minutes or so if the pump is running. So I have assumed the pump is pushing the air through.