Service engineer let the air out of expansion vessel?

[Joseph83]

I had service engineer out for my annual boiler service and I told him that about 2x a year the system will lose pressure and I have to refill it from filling loop.

He was already in the boiler at this point so he took the valve cover off the internal expansion bladder that's in the boiler and let the air out of it.

He said "that should fix it. Sometimes they get filled with air and then there's no room for the water when it expands"

That just sounds wrong to me - surely the air is there to take up space until the pressure of the water increases enough to compress the air bladder, thus giving room for expansion. With no air in it, it'll be constantly full with water, so when the water expands from heating, there is nowhere for this expansion to go? If it wasn't meant to have air in it, it wouldn't have a Schrader valve on it would it?

But he's the (supposedly qualified) engineer and I'm not, so I need a sanity check please.

 

[kidgreen61]

He's an idiot, do not let him near your boiler again.

EV should have a charge of around 1 Bar

 

[Mister Banks]

Maybe he tested the ev and the air pressure was to high so he released some of it.

 

[Joseph83]

He's an idiot, do not let him near your boiler again.

EV should have a charge of around 1 Bar

That is what I thought.

I've just recharged it to 1 bar (after de-pressurising the system)

Maybe he tested the ev and the air pressure was to high so he released some of it.

I wish what I witnessed suggested anything as calculated as that. I was chatting with him the whole time and prior to this, he didn't check the presssure at all, and when he let the air out he kept going until there was no air left to come out.

 

[Mister Banks]

That is what I thought.

I've just recharged it to 1 bar (after de-pressurising the system)



I wish what I witnessed suggested anything as calculated as that. I was chatting with him the whole time and prior to this, he didn't check the presssure at all, and when he let the air out he kept going until there was no air left to come out.

Ok ,he’s an idiot then!

 

[Johntheo5]

That is what I thought.

I've just recharged it to 1 bar (after de-pressurising the system)



I wish what I witnessed suggested anything as calculated as that. I was chatting with him the whole time and prior to this, he didn't check the presssure at all, and when he let the air out he kept going until there was no air left to come out.

Presume you precharged it to 1.0bar after de pressurising the system?, what pressure did you fill/charge it to then?, typical precharge&filling pressures would be 1.0bar/1.5bar, this then gives a reserve vol of 2.0L (assuming a 10L EV) when cold, the EV would have to leak/loose this vol of water in falling from 1.5bar to 1.0bar which means very little top ups, if ever, required, its surprising the number of boiler manufacturers who specify a precharge pressure but never specify a filling pressure, you could of course just fill it to 1.0bar but you then have no reserve leading to frequent top ups or even worse the installation of a auto filling valve to maintain this 1.0bar which means that if you get a leak you might not even be aware of it until your system starts sludging up.

 

[Harry Bloomfield]

I had service engineer out for my annual boiler service and I told him that about 2x a year the system will lose pressure and I have to refill it from filling loop.

Are you sure he was actually a qualified engineer?

 

[Joseph83]

Presume you precharged it to 1.0bar after de pressurising the system?, what pressure did you fill/charge it to then?, typical precharge&filling pressures would be 1.0bar/1.5bar, this then gives a reserve vol of 2.0L (assuming a 10L EV) when cold, the EV would have to leak/loose this vol of water in falling from 1.5bar to 1.0bar which means very little top ups, if ever, required, its surprising the number of boiler manufacturers who specify a precharge pressure but never specify a filling pressure, you could of course just fill it to 1.0bar but you then have no reserve leading to frequent top ups or even worse the installation of a auto filling valve to maintain this 1.0bar which means that if you get a leak you might not even be aware of it until your system starts sludging up.

Yeah 1 bar I charged it to.

Are you saying 1.5 bar woud be better as it gives me 0.5 bar safety margin?

 

[Joseph83]

Are you sure he was actually a qualified engineer?

Ha ha I had the same thoughts.

I checked the gas safe register: https://www.gassaferegister.co.uk/ he and his company are registered.

 

[Johntheo5]

Yeah 1 bar I charged it to.

Are you saying 1.5 bar woud be better as it gives me 0.5 bar safety margin?

Just to be clear, what I'm suggesting is that you pressurise the air end to 1.0bar, reconnect the water end to the system and then fill it until the pressure is 1.5bar, you will then have a reserve water vol of 2.0L and the final (hot) pressure will be 2.13bar assuming system contents of 100L, There is a tendency I suspect not to specify a filling pressure because, ironically, the lower the filling pressure, the lower the final hot pressure will be and the smaller the EV required, less space required in a system boiler, not to mention enhanced profits.
For example a 10L EV with precharge/filling pressures of 1.0/1.5 bar will still be sufficient to install on a system vol of 141L to give a final hot pressure of 2.5bar (comfortably below the PRV lifting pressure of 3.0br) but if the precharge/filling pressures are 1.0bar/1.0bar then a 6L EV will only have a final hot pressure of 2.23bar.

 

[Joseph83]

Just to be clear, what I'm suggesting is that you pressurise the air end to 1.0bar, reconnect the water end to the system and then fill it until the pressure is 1.5bar, you will then have a reserve water vol of 2.0L and the final (hot) pressure will be 2.13bar assuming system contents of 100L, There is a tendency I suspect not to specify a filling pressure because, ironically, the lower the filling pressure, the lower the final hot pressure will be and the smaller the EV required, less space required in a system boiler, not to mention enhanced profits.
For example a 10L EV with precharge/filling pressures of 1.0/1.5 bar will still be sufficient to install on a system vol of 141L to give a final hot pressure of 2.5bar (comfortably below the PRV lifting pressure of 3.0br) but if the precharge/filling pressures are 1.0bar/1.0bar then a 6L EV will only have a final hot pressure of 2.23bar.

Ah, understood.

Thank you, I will do that.