Air Problem in Open Vented System after Boiler Change

[ThePook]

Looks like you piped this yourself, and the GSR installer was happy to sign this off?

No, not at all. They installed to existing system. Old pipework is not great.


Air separator was installed by the GSR, after air problems started, and.because the original flow went downhill from the boiler to the vent. At that stage there was no cold feed to it. Can see the old cold feed and vent pipes cut off at the top right, but as I say, they both run compromised routes.

Only pipework changes I have made were after the air problems became apparent. I found that the (existing) vent had air traps in it so ran a new vent in 22mm uphill all the way, moving the tank to suit it's entry into the loft above a wardrobe. I ran a 15mm in alongside, so I could try separate feed/vent to see if that alleviated the problems. They take an odd route through garage as is the only way to ensure constant rise and avoid crossing joists.

The reason that the new cold feed and vent have compressions to connect to the air separator is so that I could avoid the need to fully drain down, and flush the newly soldered pipework offline before finally connecting. I simply isolated at the filter and the pump to keep the system full while I did this.

Hope this helps understand.

 

[Riley]

I think people have asked as in the normal circumstance the responsibility should be with the installers to sort it

 

[ThePook]

I think people have asked as in the normal circumstance the responsibility should be with the installers to sort it

Agreed, and understand your point.

Unfortunately, I am really not keen on the solution of sealing the system.

Thanks again all for your suggestions.

 

[Harvest Fields]

Sometimes sealing is the only option.

 

[Riley]

Agreed

 

[king of pipes]

I had a similar installation where pipe work was 30 years old buried in screed floors I upgraded the system fitted a Worcester heat only system boiler so sealed it ,also added a sealed system kit and extra expansion vessel but added a pressure reducing valve to the filling loop so I could keep the system at a low pressure thus being sealed, air is pushed out when filling and venting but does not go above 0.5 of a bar expansion is taken up in the expansion vessels and when at 65- 70 degrees c does not rise above .75 of a bar this could work for you as a last resort but I think you need to rule out any leaks on the system first. Kop

 

[ThePook]

I had a similar installation where pipe work was 30 years old buried in screed floors I upgraded the system fitted a Worcester heat only system boiler so sealed it ,also added a sealed system kit and extra expansion vessel but added a pressure reducing valve to the filling loop so I could keep the system at a low pressure thus being sealed, air is pushed out when filling and venting but does not go above 0.5 of a bar expansion is taken up in the expansion vessels and when at 65- 70 degrees c does not rise above .75 of a bar this could work for you as a last resort but I think you need to rule out any leaks on the system first. Kop

Thanks, that's a good suggestion to include an extra expansion vessel to minimise pressure increase as it heats up. If I do have to seal, I will make sure a larger one is fitted.

I completely agree that there is something else fundamentally wrong, which needs fixing itself before sealing up. That's basically where I am at, and do plan to seal in future, but only after a repipe.

I guess the part I struggle to understand is how/why sealed with 0.5bar at expansion vessel connection (presumably near boiler/pump) would make the system behave significantly differently to how it is now with approx. 0.45bar static head at the pump?

Water level in expansion tank had risen approx 6mm this morning, but system was slightly warm. Will keep an eye on it and check again at the same time and temperature.

 

[gmartine]

I guess the part I struggle to understand is how/why sealed with 0.5bar at expansion vessel connection (presumably near boiler/pump) would make the system behave significantly differently to how it is now with approx. 0.45bar static head at the pump?

No air ingress, lesser corrosion, increased efficiency and far easier to remove trapped air without the need to turn on the system.

What makes you think your pipework (which has survived for decades) won't be able to take the relatively small increase in pressure from a sealed system?

 

[gmartine]

Oh and you have a manual vent on the return, I'd probably replace that with a bottle vent which would at least prevent any trapped air from being recirculated.

 

[fixitflav]

Sorry, don't understand that, is it something I said?

Neither do I. Can't rule anything out at this stage, as the politicians say!

 

[fixitflav]

One further observation I should have mentioned above - the air seems to hide in the DHW circuit. If I manually open that zone valve, I hear the air rush into the return and filter, before hearing it again coming out of the flow,

If the HW zone valve is normally closed, sounds like the air is getting into the HW circuit via the return pipework. That might be connected with the return pipework layout you described earlier, hard to say without knowing the details. But it doesn't alter the fact that the air shouldn't be there anyway.

 

[fixitflav]

Also forgot, the condensate trap on the boiler seems to run quite often and has a black/dark dusty sediment in it. Is that normal?

That tends to support my theory - heat exchanger. Theory also means there'd be more condensate than expected, which sounds like you're getting. Can you catch it, and measure volume? Measure gas volume over same time and compare actual condensate with estimated from gas volume.

 

[fixitflav]

Finally, I notice that if I pull a small sample of water out of the boiler, it seems very foamy. Is that right for water treated with x100?

Agree with kop. Not right.

 

[fixitflav]

Water level in expansion tank had risen approx 6mm this morning, but system was slightly warm. Will keep an eye on it and check again at the same time and temperature.

Mmm! I'd expect it to drop if water is being drawn into the h/ex.

Personally, I wouldn't use pressurised on a new system, and I definitely wouldn't take out an existing F/E tank and convert. Each has its pros and cons.
And I doubt it would cure your problem. It's possible higher pressure at the boiler would stop air ingress (if that's the cause), but you might get outward leaks instead! If the pressure is kept low the boiler doesn't know it's not on gravity.

 

[fixitflav]

With respect to the boiler heat exchanger, I will try what you suggested with the tank, but would it also be possible to pressure test? I have a Monument gauge that will fit on the boiler drain terminal.

It might, but the leak only seems to happen when the h/ex is hot, otherwise you would expect water leaking out when the system is idle. BTW what's a Monument gauge?

 

[ThePook]

What makes you think your pipework (which has survived for decades) won't be able to take the relatively small increase in pressure from a sealed system?

I take your point. Honestly, its probably just a somewhat irrational fear of undiscovered leaks under floors. Genuinely, I believe it originates from discovering dry rot under the floor of our first house on day 3 of ownership, having skrimped and saved for years for a deposit, and being pennyless to sort it out quickly!

Oh and you have a manual vent on the return, I'd probably replace that with a bottle vent which would at least prevent any trapped air from being recirculated.

Good shout and an easy job for a quick win. Leave open all the time or close after initial fill and bleed? Worth putting one on the top flow into the DHW coil, too? Both places are manual at present.

But it doesn't alter the fact that the air shouldn't be there anyway.

My thoughts entirely, and why I want to remedy at source the air problem.

Mmm! I'd expect it to drop if water is being drawn into the h/ex.

What if the HEx was also somehow letting the air in? Long shot, I guess.

BTW what's a Monument gauge?

Sorry, Monument-branded water pressure gauge - on a hose with a 1/2 bsp female connector. Bought when our first house kept popping joints, and eventually proved that our incoming water mains was over 10bar at times - see above, sad times!

Thanks all for the constructive comments - appreciate you taking the time.

 

[gmartine]

A bottle vent does so automatically, yes I'd replace both manual vents. Intergas condenses all the time due to nature of hex, doesn't explain colour but may explain volume.

 

[fixitflav]

Thanks all for the constructive comments - appreciate you taking the time.

Keep us posted on F/E tank level and condensate production. I still think it's most likely the h/ex.

 

[ThePook]

Let the system cool tonight, much to the disgust of Mrs Pook, and the cold level in the tank is exactly the same as 24 hours earlier.

Going to struggle to catch and check the condensate, also cook with gas, so volumes will be misleading. Will have a think on that one...

 

[fixitflav]

Let the system cool tonight, much to the disgust of Mrs Pook, and the cold level in the tank is exactly the same as 24 hours earlier.

Going to struggle to catch and check the condensate, also cook with gas, so volumes will be misleading. Will have a think on that one...

As you do not appear to be losing water (out of the h/ex) checking condensate vs gas consumption won't tell you much.
The h/ex could still be drawing air in but not leaking water. I can't think of anything else, and you've tried nearly everything. I can see the installer will be loth to change the h/ex (or the complete boiler). Maybe if it's at your cost if it doesn't cure the problem.