Air getting drawn into sealed heating system

[marc1977]

Hi,

Ive posted this before but still not found the cause of the problem. I have a sealed S plan system with expansion tank that is drawing in air. I have to bleed one of the rads every week for 5-6 seconds. Details below:

1. The system is NOT loosing any pressure until of course I bleed the radiator. I left it alone for 3 weeks and the pressure when cold remained at 1 bar.
2. There is sentinal inhibitor in the system and i have also added sentinal leak sealant.
3. There are NO visible leaks anywhere. I have checked all rad valves and connections.
4. The expansion tank appears to be fine and has 1 bar pressure.
5. No visible leaks on the pump.
6. Worcester Bosch have been out and inspected the boiler and found no issues.

What the Damn is going on?! Have I got a magical heating system that defies the laws of science?

Many thanks

Marc

 

[Chuck]

its been about 6 months and ive bled them every week but it does seem to be very slowly improving so Im coming to the conclusion you may be correct. either that or there must be a very small leak i cant find..

I've never known a leak draw atmospheric air into a sealed pressursised system. I guess it might be possible right up close to a circulating pump that's working flat-out but even that seems to be a bit of a stretch to me.

Another possibility that hasn't been explictily explored so far is a small leak across the membrane in the expansion chamber. There's a lot of compressed air in those things and several litres of water get pushed in and out every time the system heats and cools. If you've noticed a reduction in the amount of 'air' in your system over the last month or two it could just be the warmer weather means the number of cycles of expansion/contraction has been reducing.

C.

 

[marc1977]

Yep,ive drained down the system and re pressurized the expansion tank and it seems to hold air ok. If i still have the issue in a couple of weeks i will drain it down again and check the expansion still has 1.5bar in it. sound sensible?

 

[Chuck]

Yep,ive drained down the system and re pressurized the expansion tank and it seems to hold air ok. If i still have the issue in a couple of weeks i will drain it down again and check the expansion still has 1.5bar in it. sound sensible?

Maybe, as long as the temperature is the same and you have a calibrated pressure gauge and remember that atmospheric pressure varies from day to day by about 5%.

I'd leave it a lot longer than a couple of weeks. It's easy to get obsessed with this sort of thing and cause more problems than you solve. Constantly draining and refilling the system will, for example, reintroduce air into the system every time. If you have to pump up the expansion tank once a year and bleed one radiator (because it's cold not from curiousity) twice a year I'd consider that par for the course. It's a domestic central heating system, not the space shuttle.

 

[marc1977]

Thanks again all.

 

[Harvest Fields]

Your welcome marc1977

 

[Tim Cremin]

Most people in the heating business do not know that the air is formed in the boiler when temperatures exceed 60°C. Therefore air/gas is present in all water based heating systems.
One of the reason you are witnessing air accumulating in this system maybe the boiler stat is faulty or set very high.