Boiler pressure too high when CH on

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Hi all

I have a Remeha Avanta 24s, nearly 10 years old, recently serviced with EV repressurised.

If I put CH on, the pressure goes from 1.1bar to over 3 bar within 20 mins. I've turned it off, when I do the pressure bar momentarily flickers up to nearly 4 bar, then gradually comes down.

If I put the UFH on it sits at 2.1 bar for hours, no problem. It is also fine if I put the HW on.

Any idea what is causing the pressure to go up so much, so quickly when rads on?

regards
 
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Yes, almost certainly it's an expansion vessel issue. You will need to get your boiler serviced by a gas safe engineer.
 
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It was only serviced a couple of weeks back.

How come the pressure increase for UFH and HW is ok, but goes through the roof for CH?

Does each one put different demands on the EV?
 
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Volume of the water in rads is probably greater than the water in the ufh.
 
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Did you point out the pressure issues to you service engineer? If it rises that far during warm up then I would have thought it would have been picked that up whilst doing the system checks/tests.

The fact that your system pressure increases by 1bar just with the UFH is significant, as that'll be without the rads on? It may be that when the whole system is up and running the current internal expansion capacity isn't large enough to cater for the actual amount of system water volume expansion, so may need a secondary EV.

Was the UFH added later?
 
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It was only serviced a couple of weeks back.
But there are services and services, far too many just do what we call a poke and go service, just use a flue gas analyser and go, you definately have an expansion problem
 
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@Madrab

Yes, it was pointed out at the service, no pressure in the EV so repressurised it up to 1 bar.

UFH was fitted same time as boiler (24s avanta plus) when we had renovations done 10 years ago. Yes going from 1 bar to 2 bar is without rads on.

If I turn UFH / HW off, and just run rads the pressure is going over 3 bar. I think we had the EV replaced about 5 years ago.

To be honest, when the system was working normally, it has always gone to about 2.5 bar.
 
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Thanks Picasso - would a change of boiler - to say a 30kw unit - solve this problem? Mindful that boiler is nearly 10 years old and I've no idea as to the longevity of remehas.
 
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No most boiler have a 10 litre expansion vessel and it sounds like your system is bigger than the expansion vessel in your boiler can cope with so changing the boiler wont help, get an extra vessel fitted somewhere on the return pipework .
 
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yup, +1 with @picasso.

If the installer had done some simple calculations then they should have come to the decision that the internal EV would never be able to cope with the expansion requirements of the system as a whole.

Even then, a simple monitoring of the system pressure would have told them (if they knew what they were doing) that a swing of a bar or more isn't ideal and that the system would need a secondary EV.

A remote vessel will be need to be fitted, as suggested.
 

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