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.

 

[Hoppers]

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

Thanks for the posts, John and Steadyon. Guess I am in trouble then. Should imagine finding a hidden leak is going to prove very challenging. Have a good Christmas 👍

 

[Hoppers]

Thanks for the posts, John and Steadyon. Guess I am in trouble then. Should imagine finding a hidden leak is going to prove very challenging. Have a good Christmas 👍

One final question, would using the top up loop to drain down the pressure before disconnecting the EV have any adverse affect on the pressure? I thought it was the quickest method to un-pressurise the system ?

 

[John.g]

NO.

Just re reading your posts there again.

You pre charged the EV to 24psi=1.66bar?, you don't say what the filling pressure was but say that the pressure rises to 1.5bar when hot. Except that the EV is mounted way above the boiler gauge then the pressure should rise almost instantly on heat up to 1.66bar and will fall to zero very rapidly as there is/was no water in the EV.

So, With system cool/cold, de pressurize your system again, reduce the pre charge pressure to 14.5 psi=1bar, then fill it to 1.5bar=22psi, you will then have a (reserve) volume of a few litres in the EV when cold and if the boiler pressure drops to zero very rapidly when it cools down again then you are in trouble. You can also just do the above (when cool/cold) and just monitor it without firing the boiler, the boiler pressure will start falling once (if) the water reserve is leaking away somewhere.

 

[Hoppers]

NO.

Just re reading your posts there again.

You pre charged the EV to 24psi=1.66bar?, you don't say what the filling pressure was but say that the pressure rises to 1.5bar when hot. Except that the EV is mounted way above the boiler gauge then the pressure should rise almost instantly on heat up to 1.66bar and will fall to zero very rapidly as there is/was no water in the EV.

So, With system cool/cold, de pressurize your system again, reduce the pre charge pressure to 14.5 psi=1bar, then fill it to 1.5bar=22psi, you will then have a (reserve) volume of a few litres in the EV when cold and if the boiler pressure drops to zero very rapidly when it cools down again then you are in trouble. You can also just do the above (when cool/cold) and just monitor it without firing the boiler, the boiler pressure will start falling once (if) the water reserve is leaking away somewhere.

Thanks for the advice John, very much appreciated. I will let you know how I get on tomorrow. Wife will kill me if I shut down the heating tonight and besides system will no doubt de pressurise itself overnight. Thanks again

 

[John.g]

What pressure were/have you been you filling the system to after checking the pre charge at 24psi??.

 

[Hoppers]

Thanks for the advice John, very much appreciated. I will let you know how I get on tomorrow. Wife will kill me if I shut down the heating tonight and besides system will no doubt de pressurise itself overnight. Thanks ag

What pressure were/have you been you filling the system to after checking the pre charge at 24psi??.

Just above 1 bar

 

[John.g]

Hopefully, that's the reason for rapid de pressurization, if you wish, you can increase the pressure right now by say 0.5bar (hot) but not > 2.2/2.4bar and see what the pressure is cold in the morning, you can then (should) reset the pre charge/filling pressures tomorrow at your convenience when cold by depressurizing the water side, reduce the pre charge pressure to 1 bar and refill to 1.5bar.

 

[Hoppers]

Just above 1 bar

any mileage in renewing the AAV while I am at it?

 

[John.g]

I don't think so Alvin except that its leaking water, I actually prefer to see a slight leak as you know that the nozzle is clear and generally you can just screw shut the cap on top.

 

[Hoppers]

any mileage in renewing the AAV while I am at it?

I have just topped up to 2 bar as advised and will see how things are tomorrow. I will then do as advised. Thanks

 

[John.g]

Very good, anyway, if you have a leak somewhere, you will see that 2 bar pressure falling well before the night is out.

 

[Hoppers]

I have just topped up to 2 bar as advised and will see how things are tomorrow. I will then do as advised. Thanks

Got it, thanks John. Mind you my AAV has been missing its cap for many years now. A little fluff has gathered inside but I have cleared that out.

 

[John.g]

I don't like AAV's as, unless they are passing water, you don't know whether they are choked or not which easily happens, you might be able to pick up a manual type of if you prefer the automatic type then maybe renew it if it isn't or hasn't been dribbling the odd drop of water.

 

[Hoppers]

I don't like AAV's as, unless they are passing water, you don't know whether they are choked or not which easily happens, you might be able to pick up a manual type of if you prefer the automatic type then maybe renew it if it isn't or hasn't been dribbling the odd drop of water.

John, I don’t think I have ever seen any water dribbling from the AAV. I get a squirt of water when I depress the valve on top?

 

[John.g]

A AAV has got nothing to depress on the top to my knowledge, I have cleared them out with one of my sewing needles by sticking it down through the nozzle, can you post a photo?,