Airlock?

[Unbelievable]

Hi, a week ago I drained my sealed combi system so I could remove a radiator. Having done this successfully, I refilled the system using the fill loop and the pressure has held. All the radiators filled and I bled them, I also bled the cold feed pump and the cold feed (there is a valve just before the boiler).

On restarting the system it worked for about 5 minutes and then shut down. What I did notice though was a gurgling up the pipes from the airing cupboard to the boiler. I'm now convinced there is an airlock in/around the boiler but don't know how to get rid of it.

One reason I think this is of the two water pipes entering the top of the boiler, the cold feed bleeds water (no air coming out) but the flow pipe doesn't bleed anything (no air or water). Also the gurgling noise from the airing cupboard up to the highest point in the system can only be air?

The boiler won't fire now when I send a call for heat - the pilot doesn't even attempt to light. The boiler is a Prima Potterton F, and although I have read a lot of bad things about Potterton boilers on this forum, I don't think that it's the problem. Is it something to do with the boiler being full of air that it won't attempt to light itself?

Any help would be gratefully received.

 

[Gasguru]

Firstly the Potterton Prima is not a combi boiler it is a heat only boiler - you also have a hot water cylinder.

If there is an air vent on the flow pipe and no air or water comes out it may be blocked. Depending on the type you can normally wrap towells/cloth around the pipe and remove the cap and use a pin to clear the blockage. If the boiler is downstairs the resulting water jet will hit the ceiling so hold the towell above it and protect the boiler from water ingress.

Next the boiler has probably overheated - look underneath the control panel an you should see a reset button. Pop this back in - the boiler must have cooled sufficiently for this to work.

Next shut off the gas at the meter - only turn it back on once the air has been bled from the system.

Since you have a cylinder you will have motorised valves. Run the system and switch between the how water and heating to expel the air.

Once clear of air turn the gas back on. Watch the pressure gauge as the heating heats up - check it doesn't go beyond 2 - 2.5 Bar at maximum temperature.

 

[Unbelievable]

Yes, you're right - it is a heat only boiler. I'm pretty new to all this stuff, but I'm quite handy so I thought I'd give it a go.

You've solved my problem though - it was the boiler that had overheated. I'd completely forgotten about the reset switch, so after I reset it the boiler fired and I am now toasty warm!!!!

A couple of things though. I should have stated in my original post that I live in a flat, so everything is on one floor. Also, when I said there was a gurgling from the airing cupboard to the highest point in the system, I should have said that the highest point is the boiler - all other pipes are at ground level.

Another point is that whilst reading other posts, someone mentioned about their cold feed pump settings. After resetting the boiler, I switched the pump to setting 1 - the reason being to try and force some water up to the boiler. Once the heating has cooled down again, I think I may have forced the airlock past the boiler and into the radiators, so I will bleed them and turn the switch on the pump back to setting 3 to see if it works.

The last thing I noticed is that after I have got the boiler working again, 2 of my radiators were only heating up at the top. I turned all the other radiators off and they heated all the way down to the bottom, but this suggests that I have sludge at the bottom of these two. It's not really a massive problem though as they heat eventually. If it ain't broke don't fix it and all that.

So thanks for your help Gasguru. If anyone can explain if what I've done with the pump is correct that would be good, otherwise long live DIY and thanks for having this forum!!!

 

[Gasguru]

If the radiators heat up with the others turned off you don't have sludge.

You have probably set up the lockshield valve incorrectly when you refitted the radiator. As a result the water flow is too high through this radiator and the flow through the other radiators is insufficient. Turn down the lockshield.

As you probably have a 5 meter pump, for a typical flat start on speed 1. Run the heating for 1/2 hour and check the temperature drop across the boiler and radiator pipes - should be around 10 centigrade. If its a lot more than this select speed 2. Since the weather is still mild you will not achieve accurate balancing.

 

[Unbelievable]

Thanks. I removed a radiator, not moved it, but you're right it could be the balancing.