Strange air noise and “whooshing” near pump in an otherwise efficient central heating system

[andyr123]

This is my current aerjec. The pipe you see leading out the top of it is the combined feed and vent. This is the pipe that goes into the bottom of the F&E tank.

There is no other vent pipe or indeed any pipe that goes into the loft, except the cold main, to refill the tank.

nah, that dont sound right at all then to me - I would branch off your pipe at the bottom of the tank to another pipe going above your F&E tank and bent over the top to make a proper combined F&E system then ... plus also safer if boiler should ever overheat, the water then will just boil up the vent pipe, go over the curve, into the F&E tank and fill that up and then exit outside the property by pipe just underneath the eaves and out into the back yard

or if you want to keep your air seperator thingy you could plumb like this:

 

[Plumbingnovice101]

nah, that dont sound right at all then to me - I would branch off your pipe at the bottom of the tank to another pipe going above your F&E tank and bent over the top to make a proper combined F&E system then ... plus also safer if boiler should ever overheat, the water then will just boil up the vent pipe, go over the curve, into the F&E tank and fill that up and then exit outside the property by pipe just underneath the eaves and out into the back yard

We are getting a bit off track here. But I can assure you my system is perfectly normal!

The reason it’s somewhat rare is because it’s only suitable with boilers that have overheat protection built in (like the Suprima).

There are multiple threads on this very website about it. Usually from confused people asking why their new house’s F&E tank doesn’t have a pipe over the top of it.

Google “my F&E tank doesn’t have a vent pipe over it” and you will see many threads about it.

 

[Johntheo5]

I assumed as it was a separate pipe, it could just be disregarded, as it doesn’t exist on my system!?

OK, so are you going to modify the bottom pipe from your existing set up to feed the pump, ie, flow from boiler into the top (side) of the aerjec and the aerjec bottom (side) pipe goes to the pump?.

 

[Plumbingnovice101]

OK, so are you going to modify the bottom pipe from your existing set up to feed the pump, ie, flow from boiler into the top (side) of the aerjec and the aerjec bottom (side) pipe goes to the pump?.

Correct, that’s what I was thinking, thanks to your help!

I assume I could also use the designs in figure 4 of the guide… and just cap off the cold feed inlet. I just picked figure 5 because it already had the cold feed capped off.

 

[Johntheo5]

Correct, that’s what I was thinking, thanks to your help!

I assume I could also use the designs in figure 4 of the guide… and just cap off the cold feed inlet. I just picked figure 5 because it already had the cold feed capped off.

Maybe, as you are at it, install a (manual) thumb vent where you can easily acces it, or a AAV with a isolating lever valve in order to be able to remove and clean it, as these, from my limited experience either dribble water all the time or just get blocked up.

 

[andyr123]

We are getting a bit off track here. But I can assure you my system is perfectly normal!

The reason it’s somewhat rare is because it’s only suitable with boilers that have overheat protection built in (like the Suprima).

There are multiple threads on this very website about it. Usually from confused people asking why their new house’s F&E tank doesn’t have a pipe over the top of it.

Google “my F&E tank doesn’t have a vent pipe over it” and you will see many threads about it.

I see what you mean - my kerosene oil boiler setup has a couple of overheat features, a pressure relief valve in the boilers flow pipe (its an outdoor boiler unit) that opens when water gets around 90'c - then also an electrical cut out in the burner thermostat switch for if it overheats (or normal thermostat gets stuck) it will cut out the burner, but I still like the idea if any of that fails and the water boils up then it will rise up to the pipe above my F&E tank , go into it and then exit out of the pipe underneath the roof eaves/soffit

 

[Plumbingnovice101]

I see what you mean - my kerosene oil boiler setup has a couple of overheat features, a pressure relief valve in the boiler (its an outdoor boiler unit) that opens when water gets around 90'c - then also an electrical cut out in the burner thermostat switch for if it overheats (or normal thermostat gets stuck) it will cut out the burner, but I still like the idea if any of that fails and the water boils up then it will rise up to the pipe above my F&E tank , go into it and then exit out of the pipe underneath the roof eaves

I don’t disagree, there are rumours suggesting that the reason British Gas started doing it in the 00’s was simply because it was cheaper, as they used less copper pipe!!

 

[Johntheo5]

I see what you mean - my kerosene oil boiler setup has a couple of overheat features, a pressure relief valve in the boiler (its an outdoor boiler unit) that opens when water gets around 90'c - then also an electrical cut out in the burner thermostat switch for if it overheats (or normal thermostat gets stuck) it will cut out the burner, but I still like the idea if any of that fails and the water boils up then it will rise up to the pipe above my F&E tank , go into it and then exit out of the pipe underneath the roof eaves

A vent does give a bit of comfort but even without it the combined pipe will still act as a open vented (safety) system and under normal circumstances (even with a vent) will accomodate 99% of the expanded volume, its not called a cold feed and expansion pipe for nothing.

 

[andyr123]

A vent does give a bit of comfort but even without it the combined pipe will still act as a open vented (safety) system and under normal circumstances (even with a vent) will accomodate 99% of the expanded volume, its not called a cold feed and expansion pipe for nothing.

fascinating that though because if you have got a system where you have a bent over pipe over the top of the feed tank its end is always open , not covered by water so as water heats up it expands and also pushes air out through the hole , so the air would escape through that way , just same as if you were boiling a kettle the air and heat escape safely but if you were to block a kettles spout then where would the heat and air escape it cant .

So if the OP system is like this

where the F&E pipe is at bottom of tank and covered by water then what does it do just bubble up inside the tank under the water when it needs to expand or let air out?

 

[andyr123]

Maybe, as you are at it, install a (manual) thumb vent where you can easily acces it, or a AAV with a isolating lever valve in order to be able to remove and clean it, as these, from my limited experience either dribble water all the time or just get blocked up.

a lot of AAV's these days come with a valve underneath so when you unscrew/remove the bottle part of the AAV the water shuts off so you can replace the AAV if it packs up and needs replacing, as the thread of the AAV screws back on it just automatically opens up the washer

 

[Johntheo5]

fascinating that though because if you have got a system where you have a bent over pipe over the top of the feed tank its end is always open , not covered by water so as water heats up it expands and also pushes air out through the hole , so the air would escape through that way , just same as if you were boiling a kettle the air and heat escape safely but if you were to block a kettles spout then where would the heat and air escape it cant .

So if the OP system is like this

View attachment 362533

where the F&E pipe is at bottom of tank and covered by water then what does it do just bubble up inside the tank under the water when it needs to expand or let air out?

Yes, remember the vent has the same level of water in it as the cistern so any air will have to bubble up, one way or the other, I have a isolating gate valve on the feed to the cistern ball cock and on the very rare occasions that I have to partially or fully drain the system to renew the odd TRV, to refill, I just crack this valve open, my theory is that the water trickling down one side of the 22mm cold feed will allow the displaced air to VENT up the other side of the (open) pipe, I never have the slightest problem with trapped air afterwards apart from venting the rads as per normal.

My 30L F&E cistern is (LxBxH) 15"x10"x12" so ~ 2.5L/inch height, my 85L system when fully hot will expand by around 1.4L so the level in both the cistern and the vent pipe will rise by just over half a inch say 15mm, this movement in the vent pipe isn't going to push much air anywhere.

 

[andyr123]

I'd be concerned on a system without a seperate vent pipe hanging over top of F&E header tank that someone had put a gate valve on the feed (that acts as expansion) that if they closed the valve there would be no where for air water to escape should boiler overheat

 

[Johntheo5]

You "cant" have any isol. valve on a combined vent and cold feed, it must also be not less than 22mm, but would strongly advise that a 3 bar PRV is also installed on/at the boiler.

 

[andyr123]

You "cant" have any isol. valve on a combined vent and cold feed, it must also be not less than 22mm, but would strongly advise that a 3 bar PRV is also installed on/at the boiler.

Yep our boiler, PRV fitted and no valve between F&E pipe and CH pump on the return and vent pipe lagged and goes over top of header tank and AAV fitted on flow of coil pipe of immersion cylinder

 

[Johntheo5]

Same as mine, so even if there was no vent and someone was daft enough to install and then close a isolating valve on the 22mm combined vent and cold feed, the PRV will lift and protect the boiler and more.