Air sucking IN, through expansion tank vent pipe Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[Hadyn98]

Hi,

I've seen a few posts talking about water coming out of the expansion pipe (into the the primary [smaller] tank) but I have air being sucked IN the overflow pipe (I get a small vacuum when I put my hand over it), and air coming OUT of the feed from the tank (which is in the loft).

I've also see a very little trickle of water coming out the over-flow pipe as normal.

My system is:

an Ideal Elan boiler in the kitchen, below the overflow tank
a GRUNFOS ALPHA+ pump (which I fitted today, thinking it was the previous pump)
an indirect cylinder
a 3 port (T way?) valve for selecting either radiators or h/w cylinder

Initially the boiler used to come on and off (cycling every 20 seconds to about 3 minutes), sometimes with noises (either an aeroplane diving, or knocking sounds, or gurgling).

Then, it all stopped working. The plumber that came around suggested that the boiler needs replacing, but also that the system needs a powerflush: I went for the powerflush :) . I then replaced the pump afterwards.
At least now, I'm getting hot water, and hot radiators again.

However, I am still getting noises (gurgling, but less knocking now) and the boiler still doesn't stay on for longer than 3 minutes (with cold radiators and cylinder).

Clearly I've got air in the system and I believe if I could get rid of it, I'd improve the situation a lot. My question is this:

[b]Can I extend the over-flow pipe so that its open end is underneath the water level in the over-flow tank, to prevent air being sucked back into the system?[/b] I don't want to raise the water level due to a potential overflow situation, but I don't see any problem with doing this.

If there is need to overflow, its above the level of the boiler, and if, for whatever reason, it starts to suck, it will suck water back into the system and so no air will enter the system.

Sounds logical to me, but maybe I am missing something...? Any comments greatfully received.

Thanks ,
Hadyn

[rosebery]

This needs to be taken in context of your other thread and vice versa. So first when you say:

"and air coming OUT of the feed from the tank (which is in the loft)."

what exactly are you seeing?

Cheers

[rosebery]

"Can I extend the over-flow pipe so that its open end is underneath the water level in the over-flow tank, to prevent air being sucked back into the system?"

No, no and thrice no. On your other thread its been suggested that the system may be piped incorrectly.

But the thing that really concerns me is that you are reporting air being sucked in through the vent pipe whereas the brown water would possibly indicate the opposite.

I really think you should get a reliable plumber to check it out.

Cheers

[willie gas]

hi hadyn 98 any news on tracing flow pipe from 3 port valve. sounds like system has been pumping over & drawing air in for along time. most prob from new. good luck.

[Hadyn98]

Hi Rosebery and Willie Gas, thanks for your responses.

When I filled the tank with clean water, I could see brown water entering it from the cold feed fill pipe, and eventually it was all brown again. I have also see air bubbles coming out of the fill pipe.

I have also felt a slight suction on the overflow pipe, and also seen a little (not much) water overflowing from it into the tank.

So air and water moving everywhere in both directions. I put in an inhibitor and after much bleeding the system, the noise is alot less and the boiler does run for longer periods.

I haven't traced any pipes beyond where I can see them. The cylinder, port and pump are in the airing cupboard and the boiler is in the kitchen with a hallway between them.

RoseBery: Why do you say "No, no and thrice no." to me lowering the pipe outlet under the water level in the tank? The tank is at least a 1.5m above the boiler. If there isn't any leaking from joints etc, then this is the only way that (new) air can enter the system , surely?


I will need to change the boiler at some stage, but since I've had some other big expenses recently, I'd like to just keep the current system running (sufficiently well enough) for a little longer until the cash reserves have built up again :lol:

[h]

you must keep the air gap between the water in the tank and the open vent pipe the open vent should be terminating at least 75mm? above the over flow pipe if you put it under the water level and the temp cut out does not operate the water will keep on heating and the plastic tank will melt sending boiling water though the ceiling it is sucking air because there is not enough water in the system you say you have a 3 port vale if this is not in the correct position some times the system will not fill correctly manually over ride it using the lever on the valve make shall the ball vale to the tank is working to refill the tank bled rads boiler and pump the boiler cuts out because the water is not circulating the gurgling noise is happening when the air is reaching the pump and then a wising noise when the water get there move the lever on the valve when filling a thew times you will hear when it is filling correctly bleed when cold