boiler pressure

my ideal isar he35 has been fine for the last 6 weeks since fitting until this week, i noticed the pressure had dropped to 0.75 bar from the usual 1 bar (recomended when cold) i topped it back up to 1 bar and it held this until the central heating had been on again, when it had again dropped to 0.75 bar. This has continued all week it never drops below 0.75 and works o.k. i can see no apparent leaks and the pressure release valve has not discharged any water, the maximum pressure reached when running is 2 bar. The only mention in the handbook of 0.75 bar is the pressure at which the expansion tank is pre pressurised at. has anyone any ideas

thanks in advance

Reply to
andrewd909
Loading thread data ...

Stick a pot or something under your overpressure relief pipe, and see if it fills up with water. If your expansion vessel is buggered then upon firing up, the pressure will rise, the expansion vessel will not accomodate that pressure rise and the overpressure relief valve will operate ( at about 2.5 to 3 bar ) dumping water out of the 15mm pipe that presumably emerges outside your house wall somewhere. Then belatedly you look at the system pressure and find it's dropped down to 0.75 bar.

That's one possibility anyway. If you keep filling up the system with mains water to repressurise it eventually all the inhibitor in your system will be flushed away and your boiler and radiators will start to corrode etc.

Andy

Reply to
andrewpreece

diaphragm in expansion vessel ?

RT

Reply to
[news]

I can't explain it - but it if works ok with a cold pressure of 0.75 bar, and doesn't drop any further, I wouldn't worry too much.

Reply to
Set Square

Bubbles of air from original fill working their way around the system and out of the auto vent?

Reply to
OldScrawn

See FAQ. 1.25 bar pressure rise is rather large and may indicate a partially failed (or just possibly undersized) expansion vessel.

Reply to
Ed Sirett

How many rads is it running?

My HE35 only registers a pressure rise of approx 0.8 bar going from cold to hot. That is with 10 rads.

I tend to find that my system will slowly loose a little pressure over a couple of weeks or so if you top it up to 1 bar, it takes the addition of the equivilent of a couple of cups full of water to go back to 1 bar. If you leave it, then it stabilises at about 0.8 bar. The difficulty finding such a low volume loss, is that it will probably evaporate rather than ever appear as water anyware.

On my system many of my rads are pretty old and I don't totaly trust all the valves either (I am sure the previous house owner must have cobbled together some of the collection of rads by raiding skips! - there are about three different designs). I was half expecting lots of things to start dribbling when I converted it to a sealed system, but so far nothing has actually sprung a noticable leak.

Reply to
John Rumm

Probably a dodgy or undersized expansion vessel, or simply not inflated to the correct pressure before filling the system. With a pressure rise of at least 1.25 bar, you are quite likely to run into problems.

Given the new installation, it could be either a manufacturing fault, installation fault (not checking charge pressure), or a design fault by the installing engineer who didn't calculate the capacity of the system and relied on the inbuilt vessel to accommodate expansion, when it was not up to the task and should have had an additional external vessel fitted.

Do you have a large house by any chance?

Christian.

Reply to
Christian McArdle

my house isnt particularly big more unusual 60' deep by 18' across, the boiler supplies 13 radiators + 1 towel rad. I fitted the boiler myself and was concerned at the expansion vessel section however i was assured it 'should' be o.k. my old system had 28mm flow and return pipes running to the old tank in the centre of the house 30' each i utilised these when fitting the combi boiler i intend removing them and connecting into the 22mm pipes. I think it will be best to fit an expansion vessel at the same time, just a couple of questions, can the vessel be fitted anywhere on the system,? can you recomend any particular make? would i create another problem by oversizing an expansion vessel?

Whilst i am asking, when i fitted the boiler i installed trv's upstairs, when doing the above i will probably fit an automatic bypass, what is the ideal location to fit one of these

thanks again

Reply to
andrewd909

Some boiler manufacturers state locations for the expansion vessel. However, as this is an additional one anyway, you can put it anywhere on the system that can't be valved off from the boiler. You can't (within reason) oversize an expansion vessel. I would probably calculate for a 0.5 bar rise, which gives loads of headroom.

Christian.

Reply to
Christian McArdle

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.