Air in Hot Water System?

[stoo]

Hi,

I seem to have a problem with what sounds like air in the hot water system. We have only been in the house for a couple of years and I'm sure the noise wasn't there when we moved in but I can't think when it started. The house is only about 13-14 years old. I bled the rads and a bit of air came out but nothing major.

I replaced some rads a few months back and thought that the draining down of the system and refilling might fix it but it didn't. A couple of weeks ago the pump burnt out, I replaced this with a Grundfos Alpha+ 15-50 pump hoping that this might fix the problem but it is still there.

The odd thing is that the noise of the air only appears when only the hot water is on, if you turn the central heating on, the noise peters out. Turn the central heating off and the noise comes back.

I have looked for a place to bleed the hot water but can't find anything. The noise seems to be coming from the boiler and sounds like quite large bubbles. It can't be kettling as it starts as soon as the hot water comes on. The only thing I can think of is either a problem with the boiler or perhaps the system needs flushing with fernox or something?

The system is an open vented system. Gas fired boiler (Baxi Solo WM 50/4 PF).

Any assistance with this would be gratefully received, I'm a bit stumped!

Thanks.

 

[gas4you]

If it is a fully pumped system then there should be an air bleed next to the hot water cylinder.

 

[Richsoft]

Gas, I.ve got a customers boiler doing the same thing, an Ideal Elan 2. Just makes noise on hot water. No air from bleed point so I think maybe the heat x is just scaled up. What do u think?

 

[Onetap]

Hi,

I seem to have a problem with what sounds like air in the hot water system. We have only been in the house for a couple of years and I'm sure the noise wasn't there when we moved in but I can't think when it started. The house is only about 13-14 years old. I bled the rads and a bit of air came out but nothing major.

Check the F&E tank. I think it's probably pumping over &/or sucking in air when the 3-port valve is in the HW position, but not when it's in the heating position.

Watch the open vent pipe, get someone to alter the settings on the programmer.

Do the same with a glass full of water held to the open vent, see if it sucks any in.

Probably the arrangement of boiler, cold feed, open vent and pump need revising. Could it be cold feed, boiler, open vent, & then the pump?

 

[gas4you]

Gas, I.ve got a customers boiler doing the same thing, an Ideal Elan 2. Just makes noise on hot water. No air from bleed point so I think maybe the heat x is just scaled up. What do u think?

I would have thought that at some point the boiler would make the same noise if it was scaled up even on the ch.

 

[stoo]

Hi, thanks for the replies.

It is a fully pumped system but there doesn't seem to be any air bleed! Could the 3-port valve be self venting and perhaps blocked? Not sure of the make, I'll check tonight and report back.

I haven't checked the F&E tank, again I'll have a look at that tonight and see what happens.

Thanks.

 

[stoo]

Just one other thing, the Grundfoss pump I fitted is supposed to be self venting so one would assume that this would vent the hot water?

 

[Breesey]

Just one other thing, the Grundfoss pump I fitted is supposed to be self venting so one would assume that this would vent the hot water?

If there's no finger vent you could always crack the union nut on the primary flow pipe into the cylinder, if you think there's air there to vent of course.
Did you put inhibitor in when you drained down last?

 

[PaddyBourne]

I'm no expert but whilst following some of the advice from some of the others on this forum, I found that the bleed-vent on the hot water cylinder feed was blocked.

Made quite a mess when I unblocked it!

The hot water system seems to get to temperature more quickly now.

 

[stoo]

Okay, the 3-port valve is a Landis & GYR.

I had a look at the vent pipe over the F&E tank and there was no problem there! I put a cut of water over the end and it did nothing. I guess that's good.

Breesey, I didn't put inhibitor in as I will be replacing some more rads this month. I planned to flush out the system and put the inhibitor in after this. Would that cause this problem?[/quote]

 

[Breesey]

Inhibitor will definitly reduce the build up of air in the system. It could be the reason for your problem but then again it could be something else
Did you try cracking the cylinder unions to bleed them?

When you next drain down don't forget to cut a finger vent into the cylinder flow primary!!

Put some system cleaner in a few days before you drain and flush too.

 

[stoo]

Thanks Breesey, I haven't tried cracking the cylinder unions yet. I'll give that a go and see what happens. I'll definately put some cleaner in and drain/flush it out at the weekend.

I'll post an update with the results.

Thanks for your help.

 

[stoo]

Okay, I cleaned the system out with Fernox F3 cleaner, left it running for a week then drained and flushed the system. I then treated with Fernox F1 Inhibitor and it has done the trick!! I am very surprised as it sounded so much like air in the system!

Anyhow, it's sorted now so thanks for your help.

Stoo