any central heating engineers out there?

chris954

chris954

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a couple of weeks ago our central heating boiler decided it was going to keep shutting itself down so I called the guys who fitted it and they diagnosed the pressure vessel had gone, fair enough. They replaced it with an external one thats about the size of a football and also put a new pressure relief valve in. This sorted the problem but for some reason when my central heating system is re filled, it takes weeks to get all the air out,bleeding and re filling from the tap , so as a result the pressure has been up and down all the time. This has caused the boiler to shut down a couple of times as the pressure was too low. What I need to know is what pressure (in bar) should the system be at when cold and hot? its currently about 3/4 bar cold and 2.5 hot but its been tripping out at about 1/2 bar cold and I think it would probably be more reliable with a bit more pressure but I dont want to put too much in and have it go over, blow out of the release valve and end up running too low.
 
I thought they were supposed to be 1 bar roughly when cold. Find the user manual for the boiler to check.
 
I had the same issue with my combi boiler two weeks ago, luckily the fix was to pump some air into the vessel. You need to make sure you top it up when it is cold. I have it at 1.2 when cold and it goes up to 1.6 when hot.

It needs to be over 0.8 when cold. If it falls below that you may have a leak somewhere.
 
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I fill all systems I'm commissions and servicing to 1bar when cold.
And then system can be between 1.5-2.5 bar when hot (depending on system volume and expansion vessel capacity)
The pressure relief valve they fitted should be set to relieve pressure at 3.
 
By the way thats a pre set pressure not one you can change for the pressure relief valve.
Just realised i didn't make that bit too clear.
 
The pressure vessel should be charged at 1 bar so i tend to tell customers to set the water pressure at 1 bar when cold, if its going up to 2.5 bar when hot theres something wrong. How many rads have you got and do you know the size of the external vessel they installed?
Just check its not sneaking up to 3 bar and lifting on the pressure relief valve and then when the water cools it'll be done to .5 bar or below
 
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The pressure vessle is 12 litres and we have 4x6 foot double rads 1x 6foot single,2x3foot double and 1x3 foot single
 
12 litres should be pretty muck ok, can you see which pipe they've fitted it on, the flow or return?
 
sorry I've no idea theres loads of pipes coming out of the bottom of the boiler, I presume you mean on the way into or out of the boiler, is there any way to tell?
 
Can you post an image of the boiler, with the new expansion vessel? If the pressure is still reaching 2.5 bar then something's not quite right.
 
Ben6 said:
I fill all systems I'm commissions and servicing to 1bar when cold.
And then system can be between 1.5-2.5 bar when hot.
Click to expand...

Me too.

1 bar cold usually comes up to 1.5 bar hot. 0.75 cold up to 2.5 hot seems like too much of a change.


Steve.
 
As CH and Steve have said, the pressure rise is to high, if they've fitted it on the flow the water temperature could be 75 degrees + whereas the return would be more like 55 degrees so could explain the rise, try turning the temperature dial down a bit on the boiler and see if this causes the pressure to rise less.... And let's see a pic.
 
the pressure vessel is piped in with the copper pipe on the right, the pipe its connected to feels slightly cooler than the other pipe on the left of the boiler so i assume its fitted to the return









 
Well....it's on the return pipe so that's correct, trying turning the control dial to between 1 and 2 o'clock and see what that does, are the rads very hot to touch?
 
At the setting its on now the rads are hot. If i turn the dial to 1 or 2 o'clock they are still hot but not as hot as now so I assume that would be right. It doesn't make any difference to the pressure though.
 
Just to confirm then...is that the pressure when the boilers hot, say been on an hour? And if you left it to cool what would it drop down to?
 
yes I looked at it this morning when I had to go for a "comfort break" at around 4.30 am and it was at .75 bar cold. its now at 2.5bar when hot. I turned the temperature down to about the 2 o'clock mark earlier today just to confirm what I said and its still at 2.5 bar hot.
 
I come across central heating in my job quite often- I have to fit radiators and so on.
I would not be happy with a system that reaches 2.5 bar hot. I can't say as I have come across one that has gone over 1.5 bar.

Looks like you'll just have to bite the bullet and get another heating engineer in to figure it out.
 
Forgot about this thread...
Get the person who put the expansion vessel in as it's not right, get them to drain the system and check the air pressure in the vessel and check when they've used jointing compound it's not blocked off the vessel or pipe work
 
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