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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions.

Why's my boiler gone over-pressure?



 
 
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  #1  
Old May 28th 08, 10:48 PM posted to uk.d-i-y
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Posts: 1,252
Default Why's my boiler gone over-pressure?

Alpha Combi boiler. Working fine, or so I thought.
A bit chilly this evening, so put the heating on for the first time in 3
weeks or so.
Pressure was a little low, so fill up to the recommended 1 bar. Tap is
shut off.
Heating comes on fine. 20 minutes later, I'm outside and hear water
running - the pressure relief/overflow from the boiler is spewing out a
bit more than a trickle, but less than a hosepipe, of hot water.
Back inside, turn off heating. Notice pressure guage now at 4 bar, hence
the pressure relief.
First thought, air in system, though bleeding all the rads doesnt
produce much air - typical of what I'd expect after not being done for 6
months.
Pressure now down to 2 bar when it is cool.

So, why has this happened?
The pressure relief has never opened, to my knowledge, in the 8 years
we've had the boiler.
All rads were warm, though not hot.
Thanks
Alan.
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  #2  
Old May 28th 08, 11:27 PM posted to uk.d-i-y
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Posts: 850
Default Why's my boiler gone over-pressure?

So, why has this happened?

Could be a faulty pressure vessel...
  #3  
Old May 28th 08, 11:37 PM posted to uk.d-i-y
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Default Why's my boiler gone over-pressure?

On Wed, 28 May 2008 21:48:56 +0100, A.Lee wrote:

First thought, air in system, though bleeding all the rads doesnt
produce much air - typical of what I'd expect after not being done for 6
months.


Shouldn't produce any "air" at all after a system has been in use for a
while. Routine bleeding of radiators is indicative of either lack of a
inhibitor (thus the "air" is hydrogen from corrosion of the steel rads) or
there is fresh water being introduced on a regular basis.

Pressure now down to 2 bar when it is cool.


Pressure gauge was lying initially, did you give it a little tap?

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Cheers
Dave.



  #4  
Old May 28th 08, 11:50 PM posted to uk.d-i-y
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Posts: 1,983
Default Why's my boiler gone over-pressure?

On Wed, 28 May 2008 21:48:56 +0100, A.Lee wrote:

Pressure was a little low, so fill up to the recommended 1 bar. Tap is
shut off.
Heating comes on fine. 20 minutes later, I'm outside and hear water
running - the pressure relief/overflow from the boiler is spewing out a
bit more than a trickle, but less than a hosepipe, of hot water.
Back inside, turn off heating. Notice pressure guage now at 4 bar, hence
the pressure relief.
First thought, air in system, though bleeding all the rads doesnt
produce much air - typical of what I'd expect after not being done for 6
months.
Pressure now down to 2 bar when it is cool.


http://wiki.diyfaq.org.uk/index.php?... sure_dropping

(or go to
http://wiki.diyfaq.org.uk/index.php?...Heating_Repair
and navigate to section "system pressure dropping")

--
John Stumbles

I used to think the brain was the most interesting part of the body
- until I realised what was telling me that
  #5  
Old May 28th 08, 11:56 PM posted to uk.d-i-y
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Posts: 406
Default Why's my boiler gone over-pressure?


"A.Lee" wrote in message
...
Alpha Combi boiler. Working fine, or so I thought.
A bit chilly this evening, so put the heating on for the first time in 3
weeks or so.
Pressure was a little low, so fill up to the recommended 1 bar. Tap is
shut off.
Heating comes on fine. 20 minutes later, I'm outside and hear water
running - the pressure relief/overflow from the boiler is spewing out a
bit more than a trickle, but less than a hosepipe, of hot water.
Back inside, turn off heating. Notice pressure guage now at 4 bar, hence
the pressure relief.
First thought, air in system, though bleeding all the rads doesnt
produce much air - typical of what I'd expect after not being done for 6
months.
Pressure now down to 2 bar when it is cool.



So, why has this happened?
The pressure relief has never opened, to my knowledge, in the 8 years
we've had the boiler.
All rads were warm, though not hot.
Thanks
Alan.
--
To reply by e-mail, change the ' + ' to 'plus'.



Did you remove the filler pipe after topping up the pressure?

If not tap may not have been properly closed

Tony


  #6  
Old May 29th 08, 03:28 PM posted to uk.d-i-y
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Posts: 2,490
Default Why's my boiler gone over-pressure?

In an earlier contribution to this discussion,
A.Lee wrote:

Alpha Combi boiler. Working fine, or so I thought.
A bit chilly this evening, so put the heating on for the first time
in 3 weeks or so.
Pressure was a little low, so fill up to the recommended 1 bar. Tap is
shut off.
Heating comes on fine. 20 minutes later, I'm outside and hear water
running - the pressure relief/overflow from the boiler is spewing out
a bit more than a trickle, but less than a hosepipe, of hot water.
Back inside, turn off heating. Notice pressure guage now at 4 bar,
hence the pressure relief.
First thought, air in system, though bleeding all the rads doesnt
produce much air - typical of what I'd expect after not being done
for 6 months.
Pressure now down to 2 bar when it is cool.

So, why has this happened?
The pressure relief has never opened, to my knowledge, in the 8 years
we've had the boiler.
All rads were warm, though not hot.
Thanks
Alan.


Chances are that the pressure vessel is shot [1]. That would certainly
explain the symptoms because (a) it would cause the pressure to drop
(prompting you to top it up) and then (b) it would have no resilience to
absorb the expansion volume when the system gets hot - causing the pressure
to build up to the point where it triggers the pressure relief valve.

[1] There are degrees of shottedness - some of which are fixable just by
topping up the air through the schrader valve, and some of which are not
without replacing the whole thing
--
Cheers,
Roger
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  #7  
Old May 29th 08, 05:23 PM posted to uk.d-i-y
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Posts: 1,983
Default Why's my boiler gone over-pressure?

On Thu, 29 May 2008 14:28:04 +0100, Roger Mills wrote:

[1] There are degrees of shottedness - some of which are fixable just by
topping up the air through the schrader valve, and some of which are not
without replacing the whole thing


Or more practicably by adding a new one externally, in the many cases where
you'd have to virtually dismantle the boiler to get at the one built-in.

--
John Stumbles

Bob the builder / it'll cost 'yer
Bob the builder / loadsa dosh
 




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