Immersion Loop Bleeding

[PosiDave]

please please can someone aid my frustration. I have an old style potterton boiler which heats the central and immersion heating via a timemaster valve. I have changed all rads in house recently plus towel rails. Each time I drain system and refill. Central circuit no problems all air out BUT I simply cannot get the air out of the immersion hot water side. There are only two bleeds for this one above boiler and one off the immersion outlet. Please see pictures and see if someone can help - The balance pipe is set to one turn away from off which I was advised is correct. I have bled and bled from each of the two bleeds and got nowhere and I cannot find anything that covers this - fingers crossed someone can work out how from the pictures..

View media item 92359 View media item 92360

 

[Hugh Jaleak]

Bleed 1 will vent the return pipework back into the boiler. The boiler itself should be vented via the flow pipework, assuming an open vented system. Bleed 2 should vent the cylinder coil and associated pipework, the 'balance pipe' as you call it is technically a bypass, to allow a flow through the system should the HW be off and the TRV's on the radiators shut down. Needs to be left open at least part way.

When opening bleed 2, do you get a hiss of air followed by some water?

 

[PosiDave]

Hi Ya - yes a hiss for 1 sec then water and I have bled this for 10 minutes or more and no further air comes out. Its like the water that is coming is from the central heating \I just don't seem to get the air out of the coil!! no idea how to resolve. I have even tried having the switchmaster between central and hot water hoping the air would go out a collect where I can remove like the towel rads etc.. bit still no joy

 

[Nige F]

Can you hear the air rushing round the hot water loop ?

 

[PosiDave]

yes and around the pipe down to the pump and so on. There is water in there and the tank heats without tripping out just worrying sounds of air in the water

 

[PosiDave]

please any further suggestions anyone - how I can remove air from the hot water loop ..

 

[Hugh Jaleak]

You cant do much more than open the bleed valve. Motorised valve should be set to Manual position (to hold it open to both ports) when filling to reduce the risk of air being trapped, but if the water is circulating, the cylinder is getting how and the boiler isn't cutting out prematurely and/or overheating, then there isn't much else you can do. Allow the system to run with boiler stat set to zero for an hour or 2 once refilled, it should dissipate a lot of the air out the vent pipe when circulating anyway.

If it doesn't then perhaps time to look at the vent and cold feed arrangement, wrongly configured this can actually cause the system to draw air in!

 

[simond]

Have you tried loosening the Grundfos pump screw and venting the pump?
Obvious question but there's no harm asking.

 

[simond]

PS: This system looks like its got a combined feed and vent making air difficult to purge.

 

[PosiDave]

One thing I did not do was have the switchmaster at halfway between hot water and central heating. It was set at Central heating only and I thought because of that no air would enter the hot water loop. Perhaps a refill could be worth a try. The system is 25 years old and before I touched it had no air anywhere. Agree I think the arrangement doesn't help matters but little else I can do,,, many thanks for your suggestions much appreciated. I could solve everything and buy a combi however this little potterton works fine and reluctant to swap until it throws a huge wobbly ......

Many thanks again...

 

[Hugh Jaleak]

Keep the Potterton, I'm not a great fan of combi's, whilst they have their place, it's not a one size fits all solution. I'd try initially, putting the MV in manual, and running the system (with boiler stat off so boiler doesn't fire), it should slowly start to lose the air. Don't forget to reset valve to auto and turn boiler stat up when finished!

A separate cold feed could probably be added fairly easily, needs some tube, a few fittings and soldering skills. I really wouldn't think about a refill, all you'll do is get more air into the system, you want to get out whats already in there not add more!Also, if you've drained down, you'll probably need to put fresh inhibitor into the system, but do that once you're happy you'll not need to drain it again.

 

[PosiDave]

Hi Hugh thanks for the info.. Couple of points 1) not sure how to run system as switchmaster has no manual setting its screwdriver job to turn to the Middle position then the only way the system will run is if both stats are on else switchmaster will move to the triggered stat. No idea how to run it without an ignition sorry ameteur also from the diagram where would the cold feed go out of interest which would help things I ask as putting an Essex flange on the tank soon to connect up our new pumper shower.. Appreciate Al your advise.

 

[Hugh Jaleak]

That valve may need to be at one or other positions then, no option for holding open, I'm not familiar with it so other may be able to advise. Simply the thermostat on the boiler to zero, boiler should still run the pump and system as normal but boiler just wont fire until the stat is turned up again.

Need a picture of the pipework above the pump, showing position of current vent/cold feed before advising further on that. If you're not confident with plumbing, then look at a Surrey flange rather than an Essex flange for your shower. Essex flanges can be fiddly to fit for the uninitiated.