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Air in central heating system (Read 5528 times)
thescruff
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Re: Air in central heating system
Reply #19 - Jan 30th, 2016, 10:36am
 
Stop playing with it.

Water has oxigen and when it's heated the air is released, plus you probably had trapped air when you filled it. Its normal to get the odd 10sec squirt of air for a few months.

And the pressure is supposed to rise when the boiler is turned on, worry if it doesn't go down again when cold, or goes near the 3bar mark when the htg is on.
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woodsmith
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Re: Air in central heating system
Reply #18 - Jan 30th, 2016, 9:45am
 
A brief update!

It's been 10 days since I checked the boiler and filled the system to 1.25bar ( ch cold but hw hot).

I've had very little bubbling from the pipes and the boiler has not been making gurgling noises since I upped the pressure ( from 1 to 1.25 bar). However  when I checked the pressure today it's 1.4 bar with the system cold! So I go to the rad that is first after the boiler, bleed the air out of it ( not an enormous amount of air like it used to collect but a 10 second hiss) and when I re- check the pressure it is back down to 1.25 bar.

This makes me think there is something wrong with the boiler and somehow the pump is sucking air into the system. I think I'll get in touch with Worcester Bosch and see if they have any ideas, hopefully they have seen this before.
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thescruff
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Re: Air in central heating system
Reply #17 - Jan 22nd, 2016, 12:34am
 
Logically if you don't bleed the radiators and theres no auto air vents then the pressure you be stable or drop if you have a leak/valve letting by etc.
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woodsmith
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Re: Air in central heating system
Reply #16 - Jan 21st, 2016, 4:10pm
 
thescruff wrote on Jan 20th, 2016, 4:40pm:
Set the pressure at 1to1.3bar when its cold, if you don't bleed the rads it should be easy to check whether its dropped when it goes cold.


SWMBO is not too keen on me turning the system off at the moment, especially not long enough for everything to go cold. But I have just checked the pressure with the system up to temperature and it has not dropped since yesterday. I still have no gurgling noises and everything is working perfectly, plus there is no sign of a leak anywhere or air in the rads.

Early days to be too hopeful, and I'm going to continue monitoring the pressure each day because logically there must be a leak in the system somewhere otherwise I wouldn't have needed to top the system up so much recently.
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thescruff
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Re: Air in central heating system
Reply #15 - Jan 20th, 2016, 4:40pm
 
Set the pressure at 1to1.3bar when its cold, if you don't bleed the rads it should be easy to check whether its dropped when it goes cold.
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woodsmith
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Re: Air in central heating system
Reply #14 - Jan 20th, 2016, 9:00am
 
thescruff wrote on Jan 19th, 2016, 9:27pm:
If you ain't loosing pressure you ain't got a leak  Roll Eyes


The pressure doesn't drop noticeably until I bleed the radiators then it drops a lot. Yesterday it took well over a minute to re- pressurise the system back to 1 bar by opening the valve on the filling loop.

Already tried a flame to test for hydrogen and it was definitely blowing.

This morning was the first morning where I didn't get woken up by the sound of air blowing into the radiator but I can't tell if the system is now loosing pressure. The gauge is down .2 bar but that could be because most of the system is not up to temperature.
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thescruff
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Re: Air in central heating system
Reply #13 - Jan 19th, 2016, 9:27pm
 
If you ain't loosing pressure you ain't got a leak  Roll Eyes

Next time you go bleeding radiators take a candle with you, and check whether the air is blowing or sucking.
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Re: Air in central heating system
Reply #12 - Jan 19th, 2016, 5:10pm
 
thescruff wrote on Jan 19th, 2016, 10:20am:
If your not loosing pressure you can't be loosing water


The system pressure seems to stay mostly the same as water loss is compensated by air intake. However when I bleed the radiators the pressure drops; the last time I did this it went down from 1 to 0.5bar.

Today I took the covers off the boiler and had a good look round but there is absolutely no sign of any leak. The boiler has three manual air vents but there was no air when I opened them. It probably has an auto vent ( it's an odd design but similar shape to an auto vent) but that is on the DHW storage tank. I checked the expansion tank as best I could in that it didn't feel like it had any water in it.

So then I'm left thinking I must have a leak in the house but I have a Magnclean fitted to the return next to the boiler and when I opened the bleed valve it also had no air in it.

Completely flummoxed, so I've increased the system pressure from 1 to 1.5bar, my logic is that if there is more pressure in the system it will be less able to draw air in and this seems to have worked because this evening the boiler came on with no sounds of swirling water or bubbles rushing through the pipes. Also the higher pressure will force more water out wherever the leak is so hopefully I can find it without it bringing the ceiling down!

Thanks for all the advice, this is the most bizarre central heating fault I have ever come across and I will post again if and when I finally find out if I have a leak and where it is.

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Re: Air in central heating system
Reply #11 - Jan 19th, 2016, 10:20am
 
If your not loosing pressure you can't be loosing water
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Re: Air in central heating system
Reply #10 - Jan 19th, 2016, 8:23am
 
Thanks, something else for me to look for. Not raining this morning so I shall have a good look, if anything I think the problem is getting worse so it may be more obvious.
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Re: Air in central heating system
Reply #9 - Jan 18th, 2016, 3:28pm
 
You sure have a strange one there. Assuming you top up to 1bar every time you bleed the air from the rad, I can't see how air can leak into the system anywhere, especially when it's idle. The air outside is at atmospheric pressure, it would need to be pumped in.

I'm wondering if you have a split diaphragm in the expansion tank that is sucking air through a loose filler valve each time you bleed the system therefore replacing the vacuum in the tank. I don't know, it sounds far fetched but might be worth checking.
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Re: Air in central heating system
Reply #8 - Jan 18th, 2016, 10:10am
 
thescruff wrote on Jan 17th, 2016, 10:10pm:
isolate the ballvalve or tie it up, you'll soon know whether you have a leak or not, you'd be better checking all the rad valve and pipe for signs of staining first

It's a combi. The pressure doesn't drop until I bleed the air out of the rad. I pressure tested the system as I plumbed each zone so there shouldn't be any leaks. I've been round and checked all the rad valves and there are no signs of staining or dampness.

Also I fitted a manual bleed valve on a stub pipe to the return pipe where it drops down to the boiler, I would expect this to catch any air returning to the boiler but it has little to no air in it when I open the valve.

I think the leak must be in the boiler and in the water heating loop which would account for the gurgling noises it makes when it is just set for hot water.

Cold and wet weather today not very conducive to looking, hopefully tomorrow will be better weather and I can get the panels off the boiler and maybe wrap some brown paper round the joints to see if there is any trace of a leak.
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Re: Air in central heating system
Reply #7 - Jan 17th, 2016, 10:10pm
 
isolate the ballvalve or tie it up, you'll soon know whether you have a leak or not, you'd be better checking all the rad valve and pipe for signs of staining first
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Re: Air in central heating system
Reply #6 - Jan 17th, 2016, 4:43pm
 
Headrush wrote on Jan 17th, 2016, 1:41pm:
I was always under the impression air in the boiler should automatically vent out, not pump back into the system. I know this doesn't explain where the air is coming from but have you checked the auto air vent?


Thanks for the reply but as far as I know the boiler doesn't have one, it has a few manual bleed points but no automatic one. I have thought about fitting one in the flow straight after the boiler but I'm concerned that getting air in the system is going to encourage corrosion long term. Weather should be better on Tuesday so I can get the top and front off and look for a leak without getting rained on, that's the problem with external boilers it's hard to find a slight leak in the rain Grin

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Re: Air in central heating system
Reply #5 - Jan 17th, 2016, 3:19pm
 
A lot people tighten the auto air vent in boilers as don't realise why the cap is loose!
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Re: Air in central heating system
Reply #4 - Jan 17th, 2016, 1:41pm
 
I was always under the impression air in the boiler should automatically vent out, not pump back into the system. I know this doesn't explain where the air is coming from but have you checked the auto air vent?
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Re: Air in central heating system
Reply #3 - Jan 17th, 2016, 11:08am
 
When you said air vent, I assume you meant the 15mm copper pipe from the pressure relief valve? So I put a flexible pipe from this into a glass of water and I've left this on for 24 hours but the water level hasn't changed so it looks like it isn't sucking air through this valve?

So I'm assuming you think there must be a leak somewhere on the return pipe work in the boiler on the input side of the pump? Or could cavitation cause this or can you think of anything else?

Thanks
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