Air keeps coming back in sealed heating system - no pressure drop

[sapphire]

Hi Everyone

I am new here! I hope I can get some help with a problem that I have had with my sealed system since it was installed in October 2011. I am in London SW8 and have a problem with my heating system that I have been unable to solve.

I have 2x Heatrae Sadia MEGAFLO 145litre cylinders which are indirectly heated by a Vaillant 428kw open vent boiler.Even though these were installed in October 2011 and I am still bleeding air from the system and there don't appear to be any leaks at all.

The cylinders are located in the cellar and I have 2 manual air vents in the main bathroom at the highest point of the circuit that is used to heat the water and the heating system which runs from the boiler and into the coils at the cylinders. There are motorised valves which open up to heat the radiator heating circuit radiators when heating is demanded.

It seems that no matter how much I try, I can’t get the air to leave the system. If I bleed it manually via one of the manual bleed valves, I can come back in a day and do it all again. The pressure seems to remain at 1.2 bar on the heating system no matter what I do. I am sure there is no leak at all as the pressure doesn't drop even after years, so somehow air is entering my system.

I also get air in the highest towel radiator on the top floor, which I bleed. I am thinking that as I will shut down the radiators soon, the motorised valves will only work for hot water and not the heating and so the radiators should not fill with any air.

I have thought that perhaps my expansion vessel is inadequate as I have 14 radiators currently connected to this expansion vessel. Or, perhaps the expansion vessel is faulty? I have attached pictures of the setup in the cellar and the flow/return pipes that head to the boiler. The heating water is pumped by the red Grunfos pump which has been fitted to the return of the heating system water.

The flow/return pipes do have a fair distance to travel to reach the boiler from the cylinder. They go up 1 storey and travel under the bathroom floor and then down through the kitchen ceiling directly into the boiler.

Does anyone have any ideas on what I can do? At the last service, the system was drained and more inhibitor was added (I thought that perhaps my system was low and corroding). Can I test the expansion vessel or does it seem that the problem is elsewhere?

I hope you all can help?!:yesnod:

 

[Ermintrude]

You got an open vent boiler? Or a sealed system? One or tuther

 

[AWheating]

how much air are we talking? you will always get some air buildup in the high parts of any system.

could also be gassing/ corrosion by products.

 

[IDCHAPPY]

Just a wee domestic system then? :lol:

 

[helpsy]

Any non barrier plastic pipe in system, auto air vents?

 

[Whyme]

if the expansion was knacked on the heating your pressure would drop and you'd have to refill. wheres the pressure gauge for the heating, is it in the celler. the reason i ask is if youve got a three storey house and its showing 1.5 bar in the basement you might have virtually none at the highest point and micro leaks can pull air in depending on where they are..

 

[wetdrip]

This one's gonna be a 72 to 90 posts...for sure.
Any takers; Higher, lower?

 

[sapphire]

You got an open vent boiler? Or a sealed system? One or tuther

Sorry I copied what it said on the invoice. It's a sealed system.0

 

[sapphire]

how much air are we talking? you will always get some air buildup in the high parts of any system.

could also be gassing/ corrosion by products.

Not much air if I bleed it daily. Last year I didn't bleed it and the system gurgled a lot. It was very noisy so I started bleeding it.

 

[sapphire]

Any non barrier plastic pipe in system, auto air vents?

To my knowledge it is all copper pipe but there are two rads in the kitchen and the pipes that go under the floor towards them are copper and where the come up out of the floor to the radiators they are also copper, but it is possible that they are plastic pipes under the floor. Would this have an effect?

 

[sapphire]

if the expansion was knacked on the heating your pressure would drop and you'd have to refill. wheres the pressure gauge for the heating, is it in the celler. the reason i ask is if youve got a three storey house and its showing 1.5 bar in the basement you might have virtually none at the highest point and micro leaks can pull air in depending on where they are..

Yes the pressure guage is in the cellar. The radiators do go up three stories.

 

[chris watkins]

What can't be seen from the photos is the relationship between the expansion vessel connection & the main circulator, just like open vented system it is important to ensure the system is as far as possible under positive & not negative pressure in relation to atmospheric pressure.

The connection point of the expansion vessel to the system is the neutral point, just like the cold feed on an open vented one. So the pump should be up-stream of this & as close as possible, this will ensure that all of the pipework from the outlet of the pump right round to the vessel connection will be under positive pressure i.e. greater than atmospheric when it is running.

If it is under negative pressure micro leaks in the system will allow air into the system rather than allowing water out (oxygen being smaller than water).

You really do need a good engineer to come & take a look !!

Welcome to the forum.

 

[sapphire]

Any non barrier plastic pipe in system, auto air vents?

No auto air vents - just manual

 

[sapphire]

if the expansion was knacked on the heating your pressure would drop and you'd have to refill. wheres the pressure gauge for the heating, is it in the celler. the reason i ask is if youve got a three storey house and its showing 1.5 bar in the basement you might have virtually none at the highest point and micro leaks can pull air in depending on where they are..

As the pressure guage is in the cellar, shall I increase the pressure to say 2bar?

 

[Toggles]

Id be inclined to fit Automatic Air vents.... Just to get rid of you having to do it manually, ever!
A sealed system should not be giving you this hassle. So, I'll go right back to bottom line here, as sometimes its the most basic issue and best place to start ! You say you have been bleeding the system for 4 years? If so, Im wondering if you have done this from each radiator? If so, is there a chance that when bleeding the vent you have loosened the main vent plug nut into the rad as this can happen when venting, and could easily be sucking in air with flow of water through rad. I would give these a little tighten, use adjustable spanner ( Dont over tighten though), re vent and leave, see what happens. If that doesn't work, fit auto air vents...... Best advice overall..... get in an engineer that knows what their doing to check location of pump as this could be sucking in air if it is fitted at negative position.
Good luck

 

[Ermintrude]

Id be inclined to fit Automatic Air vents.... Just to get rid of you having to do it manually, ever!
A sealed system should not be giving you this hassle. So, I'll go right back to bottom line here, as sometimes its the most basic issue and best place to start ! You say you have been bleeding the system for 4 years? If so, Im wondering if you have done this from each radiator? If so, is there a chance that when bleeding the vent you have loosened the main vent plug nut into the rad as this can happen when venting, and could easily be sucking in air with flow of water through rad. I would give these a little tighten, use adjustable spanner ( Dont over tighten though), re vent and leave, see what happens. If that doesn't work, fit auto air vents...... Best advice overall..... get in an engineer that knows what their doing to check location of pump as this could be sucking in air if it is fitted at negative position.
Good luck

If a plugs loose the 1.5 bar in systems going to make some what of. Puddle!

 

[Whyme]

As the pressure guage is in the cellar, shall I increase the pressure to say 2bar?

don't think it would hurt, give it a whirl.

 

[Toggles]

If a plugs loose the 1.5 bar in systems going to make some what of. Puddle!

Nah, Ive know many of them be a tad loose when I've installed new systems then vented or just out for the same complaint 'air in system'. Not enough for a 'puddle', just the tiniest micro leak that mostly doesn't show as heating keeps it dry. Still enough to get air dragged into system though

 

[sapphire]

What can't be seen from the photos is the relationship between the expansion vessel connection & the main circulator, just like open vented system it is important to ensure the system is as far as possible under positive & not negative pressure in relation to atmospheric pressure.

The connection point of the expansion vessel to the system is the neutral point, just like the cold feed on an open vented one. So the pump should be up-stream of this & as close as possible, this will ensure that all of the pipework from the outlet of the pump right round to the vessel connection will be under positive pressure i.e. greater than atmospheric when it is running.

If it is under negative pressure micro leaks in the system will allow air into the system rather than allowing water out (oxygen being smaller than water).

You really do need a good engineer to come & take a look !!

Welcome to the forum.

I have checked and the expansion vessel has been connected to both of the primary returns (that go into the megaflo's). The red grundfos heating pump is then connected to the RETURN pipes and is pumping the water away from the expansion vessel. Does this sound right or could this be an issue?

i thought the pump should be connected to the flow but it is definitely on the return.

I have just increased the system pressure to 2bar in the cellar as that's a good point, by the time it is on the top floor it will lose 1bar.

I have the red automatic by pass valve set to 2.5bar. Is that correct or should I change it?

Thanks for everyone's help!

 

[mike-c]

Strange! Never seen an under sink shaver point before.

 

[Jimbob]

I think the pressure is/was your problem. Although you now need an engineer to adjust the expansion vessel to suit you running at 2 bar

 

[chris watkins]

Strange! Never seen an under sink shaver point before.

It's there mike-c so all us posh southerners can pug our electric tooth bushes in to recharge.
Mind you my I found the wife's one under our basin & it seems to have been used so much all the bristles have all come out.

 

[sapphire]

I think the pressure is/was your problem. Although you now need an engineer to adjust the expansion vessel to suit you running at 2 bar

Thanks very much. I haven't found a good plumber in my area to come and rectify this! At the last service, I had the system drained and new inhibitor added and the engineer didn't touch the expansion vessel, so I am guessing that is definitely not set up correctly.

Is anyone on here happy to come and set this up for me properly? I am in London sw8.

 

[sapphire]

Just a quick update... I have increased the pressure to 2 bar and after a day, I went to bleed the tails under the sink and there was no air.

So, it looks like this might be okay now - I can't be sure. But if it is the case, where was that air coming from?

 

[Whyme]

In some cases where the pressure at the top floor of a big house is virtually nil then micro leaks can pull air into the system. now you say you've increased the pressure and no more air problems i'd look for tiny water leaks on valves etc upstairs. If air can get in a sealed system then water can get out.