Endless air in system

[Lotarogg]

I have an open gravity fed hot water system. The water is heated in a back boiler attached to a multifuel stove. The problem I'm having is air trapping in the pump and either stopping the convection when the pump is off or stopping the pump when it's running. There does seem to be a load of air as I've been releasing it constantly for two weeks. Conclusion air is getting draw in from the vent. So I sank the vent pipe into the header tank so if it did draw anything down it would be water. Still getting loads of air, any thoughts where it could possibly be coming from? Would the back boiler release it from the water when it gets very hot? I have the vent positioned before the pump and have witnesses air bubbles coming from it in the header tank.

Cheers

 

[75pete]

Is it air or gas given off from your system. When was the last time you added an inhibitor to the system, drained it down, cleaned the expansion tank out and did a simple remove and flush of the rads? It the kind of thing that us diyers can do for our selfs.
Pete

 

[Lotarogg]

It's all new Pete, apart from the backboiler. New rads and piping and cyclinder and pump. When you say gas what do you mean, the system is heated by a log fire.

My plan is at the weekend to move the air vent to position further from the pump as I can't see where else the air could be coming in.

 

[Space cat]

In normal operation you fill the system with fresh water then wait for heat to drive the air out of it. After that, very little of the tank water - which always has air dissolved in it - gets into the rest of the system. But anything that comes out of the vent must be replaced down the expansion pipe and so you have a steady supply of freshly aerated water.

Water may pump over from the vent for a number of reasons, mostly to do with poor pipe layout. Watch what happens when the pump is running but particularly when it starts or stops.

Gas in a CH system is usually hydrogen, formed by the corrosion of iron in the water. There can also be traces of hydrogen sulphide, which you'll be able to smell coming out of bleed valves.

 

[75pete]

O/k, it's new. As its anew or updated installation, it could be just a loose connection at one of the joints. Check the pump is nice and tight. Ensure that the vent is at the correct height and you have no over pumping. Did you dose the correct amount of inhibiter? Was the system given a flush when it was fitted? I would have filled and flushed at the same time then filled and run and bleed as necessary. Let it cool and drained again checking the water leaving the system. When happy, refilled with inhibiter etc.
Pete