Vent sucking in air

[dockthedanny]

Hello people, some advice required if posible.

One of my neighbours has asked me to look at her heating, she had a new boiler fitted about a year ago, and recently had a new pump fitted, now her heating is noisy, gushing noise down vent, and get so much air in system that hardly any rads get hot. She said its always been noisy, before and after new boiler. but alway heated up fine it's a baxi 616 heat only, placed downstairs. The outlet rises thru the floor, along a meter or so then up, into a t, up is the vent, along to the pump, the 2 motorised valves, hot water and heating, feed is on return to the boiler, vent is 22mm, feed is 15mm. I have put a jug of water on end of vent and it sucks it dry in no time. So I've turned the pump down as low as it will go. What are thoughts on moving feed to between the pump and vent? Would this solve the air problem?

 

[dockthedanny]

Sorry forgot to add, she had boiler serviced before Xmas, boiler man told her to have it power flushed, so she had that done too.

 

[old duffer]

so the air release valve is sucking in air rather than being a means of escape for air?

 

[dockthedanny]

There is no valve, just the vent pipe into the loft above the f & e tank

 

[cross thread]

Altering it to a ” close couple “ would be best.

 

[old duffer]

There is no valve, just the vent pipe into the loft above the f & e tank

so the expansion release pipe is sucking not blowing?

 

[Johntheo5]

The very "best" way IMO is like mine., a combined cold feed and vent but combined right up at the F&E tank, I have seen perfectly installed close coupled (and clean) systems still drawing air in until converted to my system installed from new 50 years ago with some rads 40 years old and the very odd drop of inhibitor added over the years. Can't vouch for third option that I think I came across on here.

 

[cross thread]

Some of th piping options above are only allowed on boilers with over heat protection.

 

[Johntheo5]

Yes, the combined arrangement cannot be used with a solid fuel (uncontrolled heat source) stove. All oil fired boilers have two stats, a settable control stat and a o/heat stat set to 110C/113C. I presume all gas fired boilers are likewise although I don't recall seeing a o/heat stat specifically on all the schematics I looked at?, there has to be some other means of tripping the boiler, perhaps a low pressure trip, as a sealed system if relying on the PRV could boil all the water out of the boiler (if it didn't trip) as most filling valves are shut.

I have read of some close coupled systems and allegedly clean, still drawing air in as on stopping the circ pump (external) a spurt of water comes out the vent and presumably draws in some air eventually.

 

[Dereekoo]

Poor description of system layout but if expansion vent is sucking l would suggest there is a partial blockage between inlet water feed pipe and vent pipe.

 

[Johntheo5]

Even if no blockages then because the "feed is on return to the boiler" the vent could well be under negative pressure, newer type gas boilers have a much higher pressure loss than the older types which makes matters worse so system IMO should be changed, and if close coupled system preferred, ideally as shown with both vent and cold feed (no more than 150mm apart) close to the boiler but might get away with just relocating the cold feed adjacent to the vent, no more than 150mm apart, (on the pump side as per post #1), only problem with this is part of the system may be running under negative pressure allways, tending to pull in air elsewhere if not through the vent.

 

[fixitflav]

What are thoughts on moving feed to between the pump and vent? Would this solve the air problem?

It would definitely help, that's how it should have been done in the first place.
How is it piped currently? Is the pump on the boiler flow? If it's piped boiler - cold feed - vent - pump any partial blockage between the cold feed and vent would give the symptoms you describe. Blockage can be cleared while doing the mods.
IMO it should be rectified ASAP, I dread to think what all that air being drawn in is doing to the system!

 

[dockthedanny]

It's currently pipe, boiler, vent, pump, zone valves, rads or hot water tank, then feed is on return to boiler

 

[dockthedanny]

This might be better , blue is from boiler, red is vent, green is feed from tank, purple is bypass and orange is return to boiler

 

[fixitflav]

It's currently pipe, boiler, vent, pump, zone valves, rads or hot water tank, then feed is on return to boiler

OK, that's the old way. Cold feed on the boiler return went out in the 1970s. That way the level in the vent pipe (when the pump runs) falls, by an amount equal to the boiler + some pipework headloss. If that's greater than the height from the vent connection to the feed tank top water level air will be drawn in, likely what's happening here.