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Old 11-07-2007, 12:55 PM   #1
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Central Heating advice - how do I lower the pressure ?

Hey up everyone,

I've recently had new combi boiler and central heating installed. After a few teething problems where the pressure gradually drops (due to very tiny leaks in some of the pipe joints) I've now sorted it. The guy who fitted it told me to check the pressure every so often (it must be between 1 and 2.5).
If it drops to below 1 then to turn a small screw on a pipe going into the bolier and the pressure will rise. So it did it and the pressure did indeed rise. However I have overdone it and the pressure is now 3.5

I texted him to ask how to lower it and he said I need to bleed one radiator.

I tried this but it just spirted out loads of water and didn't empty (should it empty anyway ?)

The pressure reduced and then went back to 3.5 again.

Should I bleed the radiator with the boiler turned off ?
Would the radiator empty ?
Is there another way I can reduce the pressure ?
Is it dangerous to have the pressure at 3.5 ?
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Old 11-07-2007, 01:06 PM   #2
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we have a tap on the outside of the house to bleed the system.
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Old 11-07-2007, 01:07 PM   #3
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we have a tap on the outside of the house to bleed the system.
Does yours have a maple wood handle ? Is it heated (for comfort) ?




ps anyone got any other ideas ?
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Old 11-07-2007, 01:08 PM   #4
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If you have the pressure too high, the boiler will vent excess pressure though the overflow via a pre-set pressure relief valve. Typically this will then leak and need replacing

Are you sure you've got the filling loop completely closed? If the pressure is set as high as you've said then it might take quite a bit to bring it down, keep draining the system where you can until it's down to 1 bar or so. Have you got a towel rail you could use or something - less messy?

I'd say that 1 to 2.5 bar is too high, 1.5 bar would normally be as high as any system requires - please double check this if possible.

Do you have a drain off point that you could use instead? Might be easier, stick a piece of hose onto it and gradually open it, run the pipe into a drain/toilet or bucket/outside.

If you aren't comfortable with this get someone who knows what they are doing to help.

Good luck

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Old 11-07-2007, 01:26 PM   #5
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Yes I think I do have the filling loop completely closed.

It was originally hanging loose but my mate coonnected it to the system and said it's fine but only dangerous if kids are fiddling around in there.

What would happen if I removed this ?
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Old 11-07-2007, 01:31 PM   #6
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Easy, where you opened the tap to put up a pressure is a little loop under the boiler. unscrew the end that is coupled and open the tap. The water will just flow out, a liittle milky brown in colour .Collect it in a pan and throw it away. and watch the pressure drop. I do this every 8-9 months or so.
I would advice to leave the loop hanging out so that you can just bleed the system easily .It is not a safety hazard.
If it goes too low, close the loop again and open the tap. and it goes up again. Nothing to do with radiators
central heating is a closed cycle for constant pressure. the loop opens the cycle to alleviate pressure.

Last edited by recycled; 11-07-2007 at 01:55 PM.
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Old 11-07-2007, 01:36 PM   #7
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Yes I think I do have the filling loop completely closed.

It was originally hanging loose but my mate coonnected it to the system and said it's fine but only dangerous if kids are fiddling around in there.

What would happen if I removed this ?

Nothing the loop is for bleeding the system. Have you got a baxi 80 or 105?
As long as the loop is screwed in on one side and open on the other.
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Old 11-07-2007, 01:48 PM   #8
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In my old house we had a combi boiler, must admit it was brilliant . If we over-pressurised the system we had a permanently fixed hose to drain the excess off. Trying to do it through the radiator will be messy!

If the pressure was low, we would fill slowly and gently bit by bit, leaving it for a few minutes to allow the pressure to settle as we got caught out in the same way as you on a couple of occassions . We learnt to check all the rad's for air too before adding any more water to the system so that we got a more accurate pressure reading.

We were told pressure should be no more than 1.5 bar too

hth
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Old 11-07-2007, 04:44 PM   #9
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Nothing the loop is for bleeding the system. Have you got a baxi 80 or 105?
As long as the loop is screwed in on one side and open on the other.
It's a Baxi 105. No - the loop is completely closed but I may take it out and let it dangle (as they say) - will water pour out then ?

Should the boiler be turned off when I do it ?

Sorry I'm hopeless at this type of thing.
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Old 11-07-2007, 06:31 PM   #10
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You can let it dangle. there are two pipes underneath which the loop connects into.
There are also two taps coloured black that open and shut clockwise/anticlockwise. To reduce pressure, just turn the black tap (where the loop is coming outwards open) clockwise and water will pour out, and the gauge goes down.
when it has reached the required pressure, just close the tap anticlockwise. it takes a few secs to register the correct pressure.
if you have made a mistake and the pressure is too low, then screw in the hangind side of the loop. open both taps i.e the one that you have just screwed the loop into, and the one that the loop is hanging from.
You will hear water gushing through the loop, and the pressure will start to rise again.
When you are satisfied, just close both taps and disconnect the loop, and let it hang again.
The boiler must be on while all this is going on.

Last edited by recycled; 11-07-2007 at 06:35 PM.
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Old 11-07-2007, 06:43 PM   #11
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It's a Baxi 105. No - the loop is completely closed but I may take it out and let it dangle (as they say) - will water pour out then ?


Sorry I'm hopeless at this type of thing.

No need to be sorry. Water will not pour out as long as the tap underneath the boiler that the loop is coming out of is shut.
Imagine a tap outside your house with a green hose at the end and the other end a bucket. if you open the tap, the water pours out into the bucket. If you close it it does not.
Now if you loop the green hose back into water system in your house, and you open the tap, you will just have a continuous flowing water system.
If you can identify the black taps under the boiler, let me know, if not i shall take some pics. the taps are at both ends of the pipe that the loop feeds into.
If you leave it dangling, just open the tap at the end of the screwd loop and water comes out and pressure goes lower.
Close it and water stops leaking.
To increase pressure, Close the loop and open both taps at both sides of the loop and the gauge goes up. Switch off both taps when you are satisfied with the pressure and unscrew the dangling end again. and you will be laughing
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Old 11-07-2007, 07:56 PM   #12
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Have you had a look for a pressure release valve?most likely to be next to the "loop" or near the water pump.May be coloured red. Turn that and it should vent the water outside via the copper tube that should be sticking out the wall next to your boiler.
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Old 11-07-2007, 08:10 PM   #13
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Have you had a look for a pressure release valve?most likely to be next to the "loop" or near the water pump.May be coloured red. Turn that and it should vent the water outside via the copper tube that should be sticking out the wall next to your boiler.
No need for that. he only wants to lower the pressure, or up it. If he has the baxi, he will be doing this a lot of times during different weather types,
Messing with the release valve would mean unscrewing tthe whole front frame. Doing it via the taps underneath is the way to go.
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Old 11-07-2007, 09:43 PM   #14
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HELP !!! I've nealy flooded my house !!!!

I took the pipe off to let it dangle and water shot out at high speed.

If I hadn't put a bucket under it it would have been disasterous.

I just manage to screw the pipe back on.

There is no tap to turn at the pipe end - just a small screw which I have turned before to get the pressure up.

the water is now coming through the ceiling.

oh **** it i'm leaving it at 3.5 and if it blows up tough titties
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Old 11-07-2007, 09:58 PM   #15
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Oh dear calm down i shall post some pics and you can tell me if the underneath of your boiler looks like that. 3.5 is too high to be left alone.
Do you have a little black thing, looks like a stub of plastic?
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