Pressure question regarding combi boiler

[mammoo]

Hi all,

I recently had a new worcestor 28i junior combi boiler fitted but I have a concern regarding the pressure. I just read somewhere on this forum that the water pressure should stay constant but when my heating is on the pressure rises to about 1.8 bar. The engineer who fitted it said this was normal. Was he telling the truth?

Another thing is that when the system cools it drops to about 0.8 - 0.9 bar. I topped it up a couple of weeks ago to 1 bar but it drops back to the old 0.8 after a short while. It doesn't seem to drop further than that so I don't think there is a leak. Anyone have any ideas?

Thanks

 

[ollski]

I wouldn't worry... it depends how many rads are in your system, but it's well within any limits

 

[Bahco]

Water expands when heated so the pressure will rise. How much it expands depends on how much water is in the system.

The only time to worry is if it goes above the 3 bar point.

 

[ChrisR]

If the pressure rises higher on heating it can be a sign that the precharge in the expansion vessel is reducing - leaking away slowly so there's not much room for the extra water. Get it checked at the "Annual Service" which of course you have done..

 

[doitall]

As Chris said the pre-charge of the expansion vessel should be at least equal to the static head of the system.

another problem is the expansion vessel is too small for the size of the system and requires an addional vessel.

more info required

 

[mammoo]

I'm confused now. Some people say that it is normal for the pressure to rise when the water is hot and others don't. If more information is needed then let me know and I will try and find out.

My main concern is that it keeps dropping to 0.8 after a bit when I top it up to 1. Anyone have any ideas why this might be?

Just for info:

New boiler - only fitted a few weeks ago
3 bed semi-detached house
8 rads

 

[kevplumb]

water expands app 20% wheh heated so some rise in pressure is normal


mine sits at 1 cold 2 hot

 

[Bahco]

Some people say that it is normal for the pressure to rise when the water is hot
it keeps dropping to 0.8

It is normal for the pressure to rise when hot

If it is increasing too much then the pressure vessel will need attending to.
Drop of pressure is down to a leak somewhere which will have to be found and rectified.

 

[mammoo]

The pressure only rises to about 1.8 so from what you are saying that should be ok.

Regarding the drop to 0.8 when i fill to 1.0 - is there any reason why if there was a leak it would drop to 0.8 but then not drop any lower?

Thanks

 

[Bahco]

Regarding the drop to 0.8 when i fill to 1.0 - is there any reason why if there was a leak it would drop to 0.8 but then not drop any lower?

That is a good question

 

[PEDANTICVINDICTIVEMAN]

Maybe faulty guage, when hot small amount of water going out prv then when cold drops down to 0.8 or the leak you have doesn't leak lower than that.