Open system sucking in air, closed system still sucking in air! Any help or pointers?

[fixitflav]

The cold water feed tank was literally 20cm higher than the boiler when removed and pressurising the system.

The manual you posted says 250mm minimum, but irrelevant now it's pressurised.

Page 12
Static head -
Minimum static head 250mm measured from the highest
point in the heating system (top surface of the appliance or
the highest point in the heating system) to the water level in
the feed and expansion tank

 

[Johntheo5]

The manual you posted says 250mm minimum, but irrelevant now it's pressurised.

Page 12
Static head -
Minimum static head 250mm measured from the highest
point in the heating system (top surface of the appliance or
the highest point in the heating system) to the water level in
the feed and expansion tank

Most pump manufacturers specify around 0.5M static head at the pump inlet at 75C which would mean teeing in the cold feed immediately before the pump suction if it was a OV system, the vapour pressure of water at 75C is 0.29M

 

[fixitflav]

Most pump manufacturers specify around 0.5M static head at the pump inlet at 75C which would mean teeing in the cold feed immediately before the pump suction if it was a OV system, the vapour pressure of water at 75C is 0.29M

This is about the head above the boiler, or the highest point in the system if that's higher than the boiler, not the head at pump suction.

We've discussed pump head and NPSH before! There's something wrong with your figures, at 75°C vapour pressure is 3.85m. It's 0.29m at about 23°C.
I agree that the expansion vessel (or the cold feed in an OV system) should be plumbed close to the pump suction.

 

[Johntheo5]

Came across this a few years ago and while the barrier/non barrier piping doesn't apply here, the rad valves might, I use EPH TRVs that come with a lockshield valve and these don't have a gland, just a O ring I presume, even though I've never had a problem with air ingress.

"had a long chat with Hepworth technical (Hep2O) years ago about the virtues of barrier vs non barrier pipe (in relation to oxygen crossing it). And yes non barrier pipe does let a lot more oxygen across compared with barrier but its still nominal compared with the oxygen that gets into a system via radiator valve glands- apparently its the top crossing point by a country mile for oxygen ingress. Those cheap unglanded lockshields are a death sentence for your system. Volume house contractors often use cheapo valves . Id also be looking at that."

 

[kugaman1]

Thanks, how do I know which valves are glanded?

 

[Johntheo5]

I just nipped up that glanded valve now, you can see that there was a very slight leakage, (0.5bar head from the F&E cistern) not surprising I suppose since its there for ~ 15 years or so, and its my first time nipping it up, I have vented a tiny amount of air from it say once/year, there are probably a few like that but as I never have/had the slightest problem I've never bothered checking. I suppose it would be interesting if my system was sealed to see if air would build up as it would have no open vent to escape up. I'd still be a bit surprised if thats your problem though.

 

[kugaman1]

Thanks, I guess it’s difficult to know if they are glanded before buying…

 

[dilalio]

Might be over thinking it all.
Leave it alone and see what happens.
How long before system drops to zero and stops working?
If rads get hot throughout come Heating season then no issue.

 

[Johntheo5]

Might be over thinking it all.
Leave it alone and see what happens.
How long before system drops to zero and stops working?
If rads get hot throughout come Heating season then no issue.

Post #27 seems to point to air or some (a lot of ) gas (hydrogen was ruled out) building up pretty rapidly, a video would be good, even though water is then being bled off while venting, and has to be replaced with oxygen rich raw water, its hard to imagine it causing this build up. I have completely drained down a few relations sealed systems and on refilling, after just a few ventings of the rads, absolutely no more problems, all these (oil fired) boilers are located on the ground floor. If air is being injested (with no system loss) then wouldn't the system pressure tend to rise?
The Aladdins might help as they will only release air but as the boiler is right up in the attic I think there should be a air release point installed on the boiler flow and close to the boiler top.

 

[dilalio]

Post #27 seems to point to air or some (a lot of ) gas (hydrogen was ruled out) building up pretty rapidly, a video would be good, even though water is then being bled off while venting, and has to be replaced with oxygen rich raw water, its hard to imagine it causing this build up. I have completely drained down a few relations sealed systems and on refilling, after just a few ventings of the rads, absolutely no more problems, all these (oil fired) boilers are located on the ground floor. If air is being injested (with no system loss) then wouldn't the system pressure tend to rise?
The Aladdins might help as they will only release air but as the boiler is right up in the attic I think there should be a air release point installed on the boiler flow and close to the boiler top.

"I" would leave it and worry about something else, until IF it becomes a real issue. Constantly tinkering can muddy the waters (scuze the pun).

 

[kugaman1]

Well, I’ve fitted 2 Aladdin auto vents to a couple of radiators….lets see if they help solve the problem!

 

[Johntheo5]

Any venting?, hope so!.

 

[fixitflav]

Any venting?, hope so!.

But if there is, is it a cure? Could be attacking the symptoms, not the cause. If the air ingress is still happening, and being automatically vented, there's an increased corrosion risk. The source of the air ingress is still a puzzle.

 

[kugaman1]

Trouble is, as the guy that started this thread, I’m not sure where to go next?
Seems there’s no definitive reason for the air in my system.
The heatings not being used just now as the weather is warm….Im sure we will see the issues once the heating gets used again.

 

[Johntheo5]

Even though you have checked the pump connections tight I would still install two new rubber gaskets, its a simple job that requires no drain down, even though I don't really think that the EV position (before the boiler HEX) is resulting in a negative head somewhere else in the system, you might at least think about teeing it in just before the pump.

Is the UPS2 pump a 6M or a 8M head pump and what setting is it on??
What is the normal boiler flow temperature?

You could also just wire the pump into a independent supply, manually open a zone valve and just run the pump continuously (cold) and see does air still keep building up.