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.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
DaveŁ
 
Posts: n/a
Default Fault in combi boiler's pressure guage, and/or pressure-relief valve?

I ancountered a new problem with my Brittony 80 combi boiler.

The other day, I topped up the pressure in the central heating cirquit
(to about the maker's recommended 2-bar) and then switched th boiler
back on. I happenned to notice that the pressure guage then rose to
about 3 bar, so I relieved the pressure via the pressure relief valve.


Then sometheing odd started happening. The relief valve, which is
supposed to hold pressure up to 3-bar, started blowing out water at
anything above 2 bar. I took the relief valve apart and looked inside.
All seemed in order, but when I reinstalled it, the problem continued.

Suspecting a fault in the relief valve (tired spring perhaps), I
bought a replacement today. I installed the replacement, and found
that the new valve behaves exactly the same as the old one, blowing at
2-bar instead of 3-bar.

Logic tells me (but tell me if you disagree) that the most likely
diagnosis is that the pressure guage is no longer giving a correct
reading. But if that's the case, it seems strange that the fault in
the pressure guage would happen immediately after I released the
system pressure via the relief valve yesterday, don't you think?

I guess the fault could be in the actual pressure guage dial or on the
pressure sensor from which it takes its unput. What do you think?

Thanks...

Dave L
  #2   Report Post  
Tony Bryer
 
Posts: n/a
Default

In article , DaveŁ wrote:
The other day, I topped up the pressure in the central heating
cirquit (to about the maker's recommended 2-bar)


Do they really recommend 2 bar? 1 bar should be plenty for any
2-storey house.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser
http://www.sda.co.uk/qsedbuk.htm


  #3   Report Post  
IMM
 
Posts: n/a
Default


"DaveŁ" wrote in message
...
I ancountered a new problem with my Brittony 80 combi boiler.

The other day, I topped up the pressure in the central heating cirquit
(to about the maker's recommended 2-bar) and then switched th boiler
back on. I happenned to notice that the pressure guage then rose to
about 3 bar, so I relieved the pressure via the pressure relief valve.


Then sometheing odd started happening. The relief valve, which is
supposed to hold pressure up to 3-bar, started blowing out water at
anything above 2 bar. I took the relief valve apart and looked inside.
All seemed in order, but when I reinstalled it, the problem continued.

Suspecting a fault in the relief valve (tired spring perhaps), I
bought a replacement today. I installed the replacement, and found
that the new valve behaves exactly the same as the old one, blowing at
2-bar instead of 3-bar.

Logic tells me (but tell me if you disagree) that the most likely
diagnosis is that the pressure guage is no longer giving a correct
reading. But if that's the case, it seems strange that the fault in
the pressure guage would happen immediately after I released the
system pressure via the relief valve yesterday, don't you think?

I guess the fault could be in the actual pressure guage dial or on the
pressure sensor from which it takes its unput. What do you think?


Check that the diaphragm in the expansion vessel is not holed. If it is not
holed then check the charge pressure. If low pump it back up to the makers
charge pressure.


  #4   Report Post  
EricP
 
Posts: n/a
Default

On Mon, 18 Oct 2004 17:47:44 +0100, Tony Bryer
wrote:

In article , DaveŁ wrote:
The other day, I topped up the pressure in the central heating
cirquit (to about the maker's recommended 2-bar)


Do they really recommend 2 bar? 1 bar should be plenty for any
2-storey house.


Built in espansion vessel pre-charge pressure 0.7 bar
Maximum heating pressure 3.0 bar

That the relevant bit?

Britony System II 80 Specs

  #5   Report Post  
DaveŁ
 
Posts: n/a
Default

On Mon, 18 Oct 2004 17:49:23 +0100, "IMM" wrote:


"DaveŁ" wrote in message
...
I ancountered a new problem with my Brittony 80 combi boiler.

The other day, I topped up the pressure in the central heating cirquit
(to about the maker's recommended 2-bar) and then switched th boiler
back on. I happenned to notice that the pressure guage then rose to
about 3 bar, so I relieved the pressure via the pressure relief valve.


Then sometheing odd started happening. The relief valve, which is
supposed to hold pressure up to 3-bar, started blowing out water at
anything above 2 bar. I took the relief valve apart and looked inside.
All seemed in order, but when I reinstalled it, the problem continued.

Suspecting a fault in the relief valve (tired spring perhaps), I
bought a replacement today. I installed the replacement, and found
that the new valve behaves exactly the same as the old one, blowing at
2-bar instead of 3-bar.

Logic tells me (but tell me if you disagree) that the most likely
diagnosis is that the pressure guage is no longer giving a correct
reading. But if that's the case, it seems strange that the fault in
the pressure guage would happen immediately after I released the
system pressure via the relief valve yesterday, don't you think?

I guess the fault could be in the actual pressure guage dial or on the
pressure sensor from which it takes its unput. What do you think?


Check that the diaphragm in the expansion vessel is not holed. If it is not
holed then check the charge pressure. If low pump it back up to the makers
charge pressure.


Thanks for that. How important would you say it is to check out the
integrity of the expansion vessel, bearing in mind that the boiler is
not leaking and the system seems to be working fine?

I've never delved into the expansion vessel before. I have a vague
idea where it's located, though it's not even illustrated in the
manual. Is it a big and/or skilled job, or dead simple? Any special
tools likely to be required?

Thanks again.
Dave L



  #6   Report Post  
DaveŁ
 
Posts: n/a
Default

On Mon, 18 Oct 2004 17:47:44 +0100, Tony Bryer
wrote:

In article , DaveŁ wrote:
The other day, I topped up the pressure in the central heating
cirquit (to about the maker's recommended 2-bar)


Do they really recommend 2 bar? 1 bar should be plenty for any
2-storey house.


To be more exact, the pressure guage on the boiler has part part of
the pressure scale highlighted, suggesting that the advisable system
pressure as 1 to 3 bar. The manual, on the other hand, says "Check
that the system is above 0.7 bar and below 2.5 bar, as seen on the
pressure guage".

The pressure relief valve is designed to relieve pressure at 3 bar.

What you said about 1 bar being sufficient was helpful - thanks (Yes
it is a 3-bed, 2-floor house).

Dave L

  #7   Report Post  
DaveŁ
 
Posts: n/a
Default

On Mon, 18 Oct 2004 18:00:21 GMT, EricP wrote:

On Mon, 18 Oct 2004 17:47:44 +0100, Tony Bryer
wrote:

In article , DaveŁ wrote:
The other day, I topped up the pressure in the central heating
cirquit (to about the maker's recommended 2-bar)

Do they really recommend 2 bar? 1 bar should be plenty for any
2-storey house.


Built in espansion vessel pre-charge pressure 0.7 bar
Maximum heating pressure 3.0 bar

That the relevant bit?

Britony System II 80 Specs


It sounds right, but I don't see "System II" mentioned anywhere in my
Combi 80 manual. System II may be a different Britony boiler perhaps.

Thanks

Dave L

  #8   Report Post  
DaveŁ
 
Posts: n/a
Default

On Mon, 18 Oct 2004 17:49:23 +0100, "IMM" wrote:

Check that the diaphragm in the expansion vessel is not holed. If it is not
holed then check the charge pressure. If low pump it back up to the makers
charge pressure.


PS.. If it was holed, would there not be some water leaking out? I
can't see any signs of leakage.

The pressure relief valve however, has expelled more water and now the
system is down to 0.8 bar according to the guage. (It was 2.0 bar when
I toppd up the pressure just 5 hours ago).

Dave L



  #10   Report Post  
Christian McArdle
 
Posts: n/a
Default

The pressure relief valve however, has expelled more water and now the
system is down to 0.8 bar according to the guage. (It was 2.0 bar when
I toppd up the pressure just 5 hours ago).


How much does the pressure rise when between cold and hot? If the pressure
rise is 1 bar, then the expansion vessel is either shot or undersized. It
is better to calculate a system that only gives = 0.5 bar rise and
pressurise to 1 bar when cold. With 3 storeys, the design should be more
specific and will depend on the relative vertical locations of the
components.

I suspect that if you have a system that rises 1 bar and starts at 2 bar
cold, then it will be activating the pressure relief, which may depressurise
the system considerably. The fix is to repair/add an additional vessel (if
required) and set to 1 bar cold.

Christian.




  #11   Report Post  
John
 
Posts: n/a
Default


"DaveŁ" wrote in message
...
On Mon, 18 Oct 2004 17:49:23 +0100, "IMM" wrote:

Check that the diaphragm in the expansion vessel is not holed. If it is

not
holed then check the charge pressure. If low pump it back up to the

makers
charge pressure.


PS.. If it was holed, would there not be some water leaking out? I
can't see any signs of leakage.

The pressure relief valve however, has expelled more water and now the
system is down to 0.8 bar according to the guage. (It was 2.0 bar when
I toppd up the pressure just 5 hours ago).

Dave L

Have you checked the link pipe to the expansion vessel is not blocked?


  #12   Report Post  
Ed Sirett
 
Posts: n/a
Default

On Tue, 19 Oct 2004 10:47:24 +0100, Christian McArdle wrote:

The pressure relief valve however, has expelled more water and now the
system is down to 0.8 bar according to the guage. (It was 2.0 bar when
I toppd up the pressure just 5 hours ago).


How much does the pressure rise when between cold and hot? If the pressure
rise is 1 bar, then the expansion vessel is either shot or undersized. It
is better to calculate a system that only gives = 0.5 bar rise and
pressurise to 1 bar when cold. With 3 storeys, the design should be more
specific and will depend on the relative vertical locations of the
components.

I suspect that if you have a system that rises 1 bar and starts at 2 bar
cold, then it will be activating the pressure relief, which may depressurise
the system considerably. The fix is to repair/add an additional vessel (if
required) and set to 1 bar cold.


Full info in the FAQ below.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html


  #13   Report Post  
DaveŁ
 
Posts: n/a
Default

On Tue, 19 Oct 2004 10:47:24 +0100, "Christian McArdle"
wrote:

The pressure relief valve however, has expelled more water and now the
system is down to 0.8 bar according to the guage. (It was 2.0 bar when
I toppd up the pressure just 5 hours ago).


How much does the pressure rise when between cold and hot? If the pressure
rise is 1 bar, then the expansion vessel is either shot or undersized. It
is better to calculate a system that only gives = 0.5 bar rise and
pressurise to 1 bar when cold. With 3 storeys, the design should be more
specific and will depend on the relative vertical locations of the
components.

I suspect that if you have a system that rises 1 bar and starts at 2 bar
cold, then it will be activating the pressure relief, which may depressurise
the system considerably. The fix is to repair/add an additional vessel (if
required) and set to 1 bar cold.


Funnily enough, the system seems to be working fine since I finished
the work on it yeaterday, depite the odd symptoms I mentioned:
(pressure valve blowing at 2-bar instead or 3-bar, according to the
guage). When cold, the system, reads around 1 bar on the guage and
rises to about 2 bar when hot. Does that sound about right? (it's a
smallish 3-bed house) The technical help guy at the boiler's main
office, told me the system can typically rise as much as 1.5 bar as it
gets hotter. No more water has been expelled from the pressure guage
since yesterday.

The only symptom that really puzzles me is that the 3-bar
pressure-relief valve blows at 2 bar instead of 3-bar. So did the old
one I replaced. So I suspect that the pressure guage is giving an
incorrect reading. I'm not sure how long it's ben doing that for.

I guess there is no real danger, since the pressure relief valve blows
at somwhere between 2 and 3 bar. Would you agree?


Cheers,

Dave L

  #14   Report Post  
DaveŁ
 
Posts: n/a
Default

On Tue, 19 Oct 2004 16:31:01 +0000 (UTC), "John"
wrote:


"DaveŁ" wrote in message
...
On Mon, 18 Oct 2004 17:49:23 +0100, "IMM" wrote:

Check that the diaphragm in the expansion vessel is not holed. If it is

not
holed then check the charge pressure. If low pump it back up to the

makers
charge pressure.

PS.. If it was holed, would there not be some water leaking out? I
can't see any signs of leakage.

The pressure relief valve however, has expelled more water and now the
system is down to 0.8 bar according to the guage. (It was 2.0 bar when
I toppd up the pressure just 5 hours ago).

Dave L

Have you checked the link pipe to the expansion vessel is not blocked?


No - not yet. Please see my latest reply to Christian. System seems to
be working fine, except that I suspect the pressure guage is reading
incorectly, e.g., showing 2 bar instead of 3 bar.

Dave L

  #15   Report Post  
DaveŁ
 
Posts: n/a
Default

On Tue, 19 Oct 2004 18:34:45 GMT, (DaveŁ) wrote:

On Tue, 19 Oct 2004 10:47:24 +0100, "Christian McArdle"
wrote:

The pressure relief valve however, has expelled more water and now the
system is down to 0.8 bar according to the guage. (It was 2.0 bar when
I toppd up the pressure just 5 hours ago).

How much does the pressure rise when between cold and hot? If the pressure
rise is 1 bar, then the expansion vessel is either shot or undersized. It
is better to calculate a system that only gives = 0.5 bar rise and
pressurise to 1 bar when cold. With 3 storeys, the design should be more
specific and will depend on the relative vertical locations of the
components.

I suspect that if you have a system that rises 1 bar and starts at 2 bar
cold, then it will be activating the pressure relief, which may depressurise
the system considerably. The fix is to repair/add an additional vessel (if
required) and set to 1 bar cold.


Funnily enough, the system seems to be working fine since I finished
the work on it yeaterday, depite the odd symptoms I mentioned:
(pressure valve blowing at 2-bar instead or 3-bar, according to the
guage). When cold, the system, reads around 1 bar on the guage and
rises to about 2 bar when hot.


PS Slight correction: I looked at it at night, after the rads had
stoped heating and the pressure was down to almost 0-bar on the guage.
However it still fired up when I turned a hot tap on. I have now
topped up the pressure to 1 bar while it was relatively cool.

Dave L
Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Ravenheat Combi Boiler Simes UK diy 22 April 2nd 04 01:03 AM
Ferrolio Optima 901 relief valve test knob Ted UK diy 3 January 8th 04 04:12 AM
Gas Combi Boiler Pressure Relief Pipework & Building Regs Mitch UK diy 8 December 7th 03 12:11 PM
Replacing Pressure relief valve on Baxi Boiler Andy UK diy 0 November 27th 03 03:59 PM
single check valve pressure drop Matthew Barnard UK diy 1 July 24th 03 09:00 PM


All times are GMT +1. The time now is 09:15 AM.

Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 DIYbanter.
The comments are property of their posters.
 

About Us

"It's about DIY & home improvement"