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

 

[Harvest Fields]

How many radiators do you have? are they small or large? Are they doubles or singles and how much inhibitor did you put in to the system?

 

[marc1977]

Its a big house..15 rads with 2 very big doubles rest are singles. Lots of drops too if that helps as downstairs floor is concrete.

I put 1.5 bottles of sentinal in.

Also Ive tried igniting the gas but it didn't ignite so dont think its hydrogen.

 

[Harvest Fields]

Sentinel x100 is a good inhibitor but for a system your size I would use 2 x 1 litre bottles. As a 1 litre bottle only does 8-10 rads have you have the condition of the water in the radiators tested?

 

[marc1977]

No. I should mention all the rads are new and the system was drained down and refilled 6 months ago. Most of the pipe work is new too. Can you buy testing kits for the water?

 

[Jay The Plumber]

did you check the expansion vessel pressure when the system pressure was at 1 bar or did you drop the system pressure to check it?

 

[marc1977]

i did it when the system was cold.

 

[Jay The Plumber]

i did it when the system was cold.

and the system pressure was at 1 bar cold ?

you normally need to drop the system pressure below the pressure that the expansion vessel is charged to.

 

[Last Plumber]

Where is the pump in relation to the expansion vessel ?
Can you post a photo of the installation of the pump and vessel?

What pipe material is it?
If it is plastic, is it the correct one (barrier) ?
Most of it is these days but you never know !

 

[marc1977]

Last Plumber,

Photo attached. All pipework is copper.

Jay,

So the expansion vessel has to be below the pressure of the system??

 

[Jay The Plumber]

@marc1977 - yes the system pressure needs to be dropped below the pressure inside the expansion vessel otherwise you are just reading the system pressure.

 

[Last Plumber]

No leaks around the boiler ?
Look at pipes and fittings from tee of exp vessel to rear of pump via Boiler,
When it's cold and not working.

To work on the boiler you need to be gas safe registered so if you cannot see the pipe joints at the back, you'll need a Gas Safe registered Engineer.

 

[Jay The Plumber]

check all the drain offs, if they aint tight they can pull in air. check for them around the boiler and also on the rads, tighten the valve (square nut) and the outer knurled 'nut'
let us know if any were loose

 

[marc1977]

ok, checked all of those and cant see ANY leaks or loose nuts.

I drained the system down to release the pressure in order to properly check the expansion tank pressure. It now looks like the expansion tank was probably slightly under pressure before so have pumped it up to 1.5 bar.

I let all the air out of the expansion vessel first and there was some moisture in the air that was released..it was only spitting a small of water though. i wonder if this is normal?

 

[JCplumb]

You mention you have drained down and also that the radiators are quite new so the system was drained down when they were installed. Air is common in systems that have been drained down, you have a big system too which increases the potential for air remaining in the system after refilling.
How many times have you bled the rads after the latest drain down? Depending on your pipe runs, it could be quite normal that you need to bleed half a dozen times or so after work has been carried out or system has been drained/refilled.