Combi boiler pressure falls to 0.5, rises to 1.9 bar when heating is on

neilmcl

Mrmarc wrote: »

Hi all

Thanks for the responses, very helpful indeed.

I've not topped it up myself as I'm thinking it it's gone down only 3 days after being set at the correct pressure, that must indicate a fault?
Does anyone know if the pressure should rise if heating is off, but I'm running the hot water? It does this (slightly)
The guy I had look at it fix it reckons (based on my email description) it's the filling lock passing hot water into the heating system, which caused it to overflow, and loose pressure. Reckons it'll need a new valve. I don't think boiler is that old (maybe from 2012).
Does that sound reasonable?

Appreciate all the help

I think the first thing you should do is make sure you've bled all your radiators then fill the pressure back up until it reads 1 bar minimum. Then keep an eye on it over a week or two. If it drops significantly in that time then you'll know you have a problem.

Again, what make/model of boiler?

Ruski

Mrmarc wrote: »

Hi all

Thanks for the responses, very helpful indeed.

I've not topped it up myself as I'm thinking it it's gone down only 3 days after being set at the correct pressure, that must indicate a fault?
Does anyone know if the pressure should rise if heating is off, but I'm running the hot water? It does this (slightly)
The guy I had look at it fix it reckons (based on my email description) it's the filling lock passing hot water into the heating system, which caused it to overflow, and loose pressure. Reckons it'll need a new valve. I don't think boiler is that old (maybe from 2012).
Does that sound reasonable?

Appreciate all the help

If the fill loop was letting by, the pressure would eventually get up to 3 bar, the PRV would let by for safety, causing the outside pipe to drip. It would maintain this pressure and the boiler (in all likelihood) would refuse to fire up.
As your's gets up to 0.5 bar when cold, then rises when fired up, we can discount that theory.
A rise of 1.2 bar is not critical, as long as it doesn't go towards the 3bar mark.
I would suggest from your descriptions that the Pressure vessel needs topping up (think of it like a bicycle inner tube which needs pumping up on occasion as Bris has said), or you need to add another to the system, if it is a large system and hasn't been designed correctly.

HTH

Russ

Mrmarc

Thanks this makes perfect sense.
The make/model is a Flexicom CX 30.

It's a small system, 1 bedroom flat, 4 rads including the towel rail.

Mrmarc

Also I should add radiators were bled at the time of the last repair.

JimmyChanga

Also I should add radiators were bled at the time of the last repair.

Don't rely on that. You need to check well after a repair/refill as fresh cold water will hold more oxygen that will eventually come out to the top of rads. Also the automatic air vent in the boiler will have released some too over time. This will drop the pressure of the system.

Unlikely filling loop issue as it would eventually come out of pressure release valve as said above. Is it a temporary braided hose filling loop? Then it should not be attached anyway. Plus you'll know if it's leaking then.

Going up to 1.9 bar is not a problem. It should be going up as it heats. But for a small 4 rad system it should normally be lower. So your boiler expansion vessel may need topping up with air.

Overall you need to get confident in doing stuff yourself. I'm getting the impression you don't want to touch anything like refilling and bleeding rads. Tons of videos on youtube giving you advice on how to do this stuff. In my day we had to work it our ourselves! :-)

neilmcl

Mrmarc wrote: »

Thanks this makes perfect sense.
The make/model is a Flexicom CX 30.

It's a small system, 1 bedroom flat, 4 rads including the towel rail.

Easy to fill up then.

https://www.youtube.com/watch?v=0Fz5-z6_ATc

southcoastrgi

Put the pressure upto 1 bar when it's not runnng

Mrmarc

Thanks for this video. The sticker on my boiler has instructions for this but talks about connecting hose which I don't have. I followed the instructions in the video and the pressure went from 0.5 to 1.1 in about half a second. No hose needed at all.
Left it off over night and it was at 1.0 this morning, and had have the heating on nonstop for an hour today and it got as high as 2.0. I'm hoping that means job done for now, I'll see how it goes over the next few days.

Thanks again for all the replies.

Mrmarc

JimmyChanga wrote: »

Overall you need to get confident in doing stuff yourself. I'm getting the impression you don't want to touch anything like refilling and bleeding rads. Tons of videos on youtube giving you advice on how to do this stuff. In my day we had to work it our ourselves! :-)

Agree - software engineer by day so I'm use to the comfort of an 'undo' button :rotfl: