Vented CH system: Change to pressurised to solve air problems?

[BlueLoo]

Hello.

I have constant air in my CH system.

System:
Open vented fully pumped system with combined F-E as per boiler IOM. Boiler is a non condensing Suprima 50.

I've tried everything i know or read about and have been chasing the work of the ******s who originally put in the system for the last 20 years.

Everything i try has failed.

Some observations:
* It's air, not hydrogen.
* The system is clean, with ample inhibitor.
* Air vents etc installed at the system high points don't solve the problem.
* Pump is on boiler feed side.
*I see no leaks.
* I don't see significant water changes in the head tank

I think air is being sucked in somewhere. Two main culprits would be the actuated valve glands, or, the piping which is buried in the ground floor slab.
Pump is new and my TRVs are good quality. (Doesn't eliminate them though).

I'm fed up with it so i think i might change to a pressurised system.
Reading on this site, this seems to be a last ditch solution.

I have thought about putting sealer in the water to stop any leaks under the slab if thats the issue but i dunno. My boiler is old so thats not really an issue but still, its a bodge fix.

Any thoughts?

If this is good solution, any pitfalls or can i just add a pressure guage and expansion tank and hey-ho?

It's either this, or start ripping up floor boards and just fully replumb the whole thing as it should have been dine when installed.


Conments appreciated

 

[Mottie]

Even when I had my system converted to sealed, I still had air percolating around the system until I fitted a Spirovent de-aerator. I dont know if they would work in a vented system though.

 

[BlueLoo]

Even when I had my system converted to sealed, I still had air percolating around the system until I fitted a Spirovent de-aerator. I dont know if they would work in a vented system though.

Thanks.

I had this down to fit but thought perhaps I'm chasing ghosts so am considering switching to the pressurised set up.

Might give it a go as a last ditch attempt.

So frustrating.

 

[Johntheo5]

Is the combined F&E like mine below, the very best type IMO, some rads are > 40 years old.

 

[BlueLoo]

Is the combined F&E like mine below, the very best type IMO, some rads are > 40 years old.

It was.

I removed the vent overflow pipe recently because investigation suggested it was a good idea (Std practice for BG) and it was the exact setup recommended in the boiler iom.

Made a huge difference. No more pull down in pump start up but the air ingress still remains.

I costed up a new pressurised hw tank for changing to pressurised system.

Eek.

Might just give the spirovent a lash before going down this road.

 

[Johntheo5]

Have you checked the pump inlet&outlet connections, these can draw in air (especially on the inlet (suction) side), it might be worth isolating the pump if the isolating valves are of the type with a spindle and gland nut and not the ball type with a allen key type shut off , and replacing the gaskets with rubber ones.

What make of pump/model/mode/setting are you running on?.,

 

[BlueLoo]

Have you checked the pump inlet&outlet connections, these can draw in air (especially on the inlet (suction) side), it might be worth isolating the pump if the isolating valves are of the type with a spindle and gland nut and not the ball type with a allen key type shut off , and replacing the gaskets with rubber ones.

What make of pump/model/mode/setting are you running on?.,

Interesting comment.

It's a DAB evosta2 with gate valves. (The old ball valves nearly flooded my kitchen!)

Running on PP level 2.
(Level 1 isn't strong enough)

It's a newish pump but I'll have another look the the connections.

 

[BlueLoo]

Actually, I'll check all joints downstream of the neutral point to make sure they are secure and not sucking air in

 

[Madrab]

Suprima's, great little boxes, bullet proof HEX's. Getting older now depending on when it went in.

A combined was always considered more of an alternative that would be used with a low head installation on low level buildings, bungalows etc or to try and stop air being drawn in when a system was becoming restricted, usually at the . If it was a normal 2 storey house with attic space then a standard 2 pipe feed and vent was preferable. TBH a well designed system shouldn't need a combined feed/vent, as they can sometimes interfere with the normal expansion (breathing) feature which a vented system is designed to incorporate. They can also be a real pain to fill and can actually trap air in the system.

Does your system have an air separator?

No reason you can't go to a sealed system, wouldn't say it's a last ditch attempt, though if it is drawing in air and it's not through the feed/vent then that would usually show up as a leak if the system was then sealed.

 

[BlueLoo]

Suprima's, great little boxes, bullet proof HEX's. Getting older now depending on when it went in.

A combined was always considered more of an alternative that would be used with a low head installation on low level buildings, bungalows etc or to try and stop air being drawn in when a system was becoming restricted, usually at the . If it was a normal 2 storey house with attic space then a standard 2 pipe feed and vent was preferable. TBH a well designed system shouldn't need a combined feed/vent, as they can sometimes interfere with the normal expansion (breathing) feature which a vented system is designed to incorporate. They can also be a real pain to fill and can actually trap air in the system.

Does your system have an air separator?

No reason you can't go to a sealed system, wouldn't say it's a last ditch attempt, though if it is drawing in air and it's not through the feed/vent then that would usually show up as a leak if the system was then sealed.

Thank for the reply.
Very interesting.

The boiler is indeed simple but effective. Never had an issue with the cast iron he-ex. PCBs are a different story!

Putting in proper Feed and expansion lines is effectively impossible. The boiler is in the kitchen and no local feed or expansion piping was ever installed.
A 22mm pipe was simply added to the feed on the hot water tank and sent up to the attic tank.

Reconfiguring as best i can, I've managed to change one of the upstairs feed lines to a proper Combinded FE .

You're probably wondering how or what that means?
I think it was apprentice day when this house was plumbed up. Wrong pipes, going to wrong things all over.

Anyway, you're the second person to mention an air seperator.

I'll give it a go.
Not sure where to fit it in though!

 

[Madrab]

Anyway, you're the second person to mention an air seperator.

I'll give it a go.
Not sure where to fit it in though!

If it's a purpose made separator like a spirovent then on the outlet of the boiler would probably be best, if it's an old style can type then probably wouldn't work properly with a combined as they use use the up and over vent.

 

[BlueLoo]

If it's a purpose made separator like a spirovent then on the outlet of the boiler would probably be best, if it's an old style can type then probably wouldn't work properly with a combined as they use use the up and over vent.

On the outlet?

Ooh, i might have enough room for that with a spirovent.

 

[Madrab]

On the outlet?

Yes, they recommend to be placed as close to the hottest point on the system, presumably as it's where most of the air would be found.

 

[martygturner]

we used https://www.toolstation.com/aladdin-auto-airvent/p45273 on the rads problem disappeared..

 

[fixitflav]

I costed up a new pressurised hw tank for changing to pressurised system.

You can convert the primary circuit to pressurised without changing the HW cylinder. The primary and secondary circuits can be open vented or pressurised in any combination.
Not quite clear about your layout. Is it boiler - open vent - cold feed - pump? (for separate vent and feed) so the pressure reference point is close to the pump suction? If so, there should be no points at negative pressure, which could cause air ingress.