Pressure loss in Heating System post fitting new Expansion Tank

[Hoppers]

Hi, hope someone can help me with a heating pressure loss problem. My valiant boiler has been loosing pressure over the last few months, resulting in me having to top up the water every week or so. Managed to get a boiler engineer to visit who diagnosed a faulty expansion tank. (Water evident at the valve on top of the EV). I replaced the EV but now the pressure drops to zero within a few hours. I’ve bleed all radiators and there are no visible leaks. Boiler working very well also and the EV was correctly charged when it arrived. If water spurts out of the Auto Air Vent (bottle type) when I depress the valve at the top does that mean it is faulty and would this affect my system pressure. The vent does not leak but perhaps it is not venting the system properly. Grateful if anyone can help. Thanks Alvin

 

[steadyon]

1. Where is the Auto Air Vent (AAV) you refer to fitted on your system?
2. What was the air pressure in the EV before fitting, and was it altered after fitting?

The AAV should bleed air in the system as that air reaches the AAV. If you depress the valve at the top it should produce water, any air having already been bled. Sounds as if that is what you have, and if so, then the AAV is doing its job.

Have you checked that the boiler's pressure relief valve is not opening / dribbling? Test if there is any water coming out of the pressure relief pipe. This is normally copper, goes outside, and has its open end turned back against the wall.

What Vaillant model boiler do you have, and specifically is it a combi, system boiler, or open vent boiler on a sealed heating system?

 

[Hoppers:]

Hi Steadyon, thanks for getting back to me. The boilers is a Vaillant eco TEC Condensing boiler. The AAV is situated between the actuator switch and the Emerson Tank.
I tested the pressure of the EV before fitting (Tuesday) and it read 24psi. Tested again a couple of hours ago and pressure still 24psi.
Boiler pressure relief valve not leaking, tested before buying new EV and again on a daily basis as I struggled to work out why pressure dropping. During boiler operation, pressure climbs up to just above 1.5 bar but once the boiler switches off the pressure then drops over an hour or two to close to zero. Before fitting the new EV the pressure would take at least a week to fall to zero, but now it drops to zero during the night.

 

[Hoppers]

1. Where is the Auto Air Vent (AAV) you refer to fitted on your system?
2. What was the air pressure in the EV before fitting, and was it altered after fitting?

The AAV should bleed air in the system as that air reaches the AAV. If you depress the valve at the top it should produce water, any air having already been bled. Sounds as if that is what you have, and if so, then the AAV is doing its job.

Have you checked that the boiler's pressure relief valve is not opening / dribbling? Test if there is any water coming out of the pressure relief pipe. This is normally copper, goes outside, and has its open end turned back against the wall.

What Vaillant model boiler do you have, and specifically is it a combi, system boiler, or open vent boiler on a sealed heating system?

 

[Hoppers]

Thanks for getting back to me Steadyon. I am having problems with this site as I have written a response and sent it but doesn’t look like it survived contact with the internet. I will try agai.
My boiler is a Vaillant eco TEC condensing boiler. Fitted in Feb 2011
The AAV is fitted between the directional auctuator valve and the Emerson tank.
I tested the new EV before fitting (24psi) on Thursday last week and again today 24psi.
The PRV is working fine as no dripping from the discharge pipe outside.
Before fitting replacement EV the pressure would take over a week to drop to zero but now it does it over night. I find myself getting up early hours to ensure I top the system up befor the boiler switches on at 7am.
I should have added on my original post that once I had fitted the new EV I also took the opportunity to add 500ml of inhibitor to the system.

 

[Hoppers]

Thanks for getting back to me Steadyon. I am having problems with this site as I have written a response and sent it but doesn’t look like it survived contact with the internet. I will try agai.
My boiler is a Vaillant eco TEC condensing boiler. Fitted in Feb 2011
The AAV is fitted between the directional auctuator valve and the Emerson tank.
I tested the new EV before fitting (24psi) on Thursday last week and again today 24psi.
The PRV is working fine as no dripping from the discharge pipe outside.

 

[John.g]

After you have topped it up/checked pressure at 24PSI, what pressure does it rise to when system is hot?.

 

[Hoppers]

After you have topped it up/checked pressure at 24PSI, what pressure does it rise to when system is hot?.

Just above 1.5 bar

 

[Hoppers]

Just above 1.5 bar

Sorry 1.5 was the heating side pressure. When I last checked the EV the system was hot and the reading was 24psi. Before I initially fitted the new EV the cold pressure was 22 psi as I recall

 

[John.g]

PRV isn't leaking you said and boiler pressure way below 3bar so unfortunately looks like a leak somewhere.