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Old 17 October 2004, 20:52   #1
Kev_turbo
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Default combi boiler drops pressure when kicks in

Hi,

Advice needed please from the resident plumbers.

Running a combi boiler (C+M Britany combi 80) that had been installed in the last couple of years but over the last week or so we have started having the odd problem.

1. The boiler is steadily losing pressure requiring a top up every 3-4 days from 0.5bar to 1.5bar.

2. When the timer kicks in and the unit lights there seems to be a sudden drop of approx 0.5bar which slowly picks back up as the water heats up (is this just expansion)

Questions.

1. Is the general drop in pressure just likely to be a leak somewhere? If so what is the best way to find it without ripping up floors?

2. What could be causing the sudden drops in pressure?

3. Is it worth paying out for the british gas insurance thing, i.e. is the boiler likely to go pop?

Notes.
There isn't any noticable leak on the boiler unit itself.
There is no discharge from the overflow/blow off pipe.
All radiators are hot and bleed

Thanks in advance

Kev
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Old 17 October 2004, 22:10   #2
Mog
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Quote:
Originally Posted by Kev_turbo
Hi,

Advice needed please from the resident plumbers.

Running a combi boiler (C+M Britany combi 80) that had been installed in the last couple of years but over the last week or so we have started having the odd problem.

1. The boiler is steadily losing pressure requiring a top up every 3-4 days from 0.5bar to 1.5bar.

2. When the timer kicks in and the unit lights there seems to be a sudden drop of approx 0.5bar which slowly picks back up as the water heats up (is this just expansion)

Questions.

1. Is the general drop in pressure just likely to be a leak somewhere? If so what is the best way to find it without ripping up floors?

2. What could be causing the sudden drops in pressure?

3. Is it worth paying out for the british gas insurance thing, i.e. is the boiler likely to go pop?

Notes.
There isn't any noticable leak on the boiler unit itself.
There is no discharge from the overflow/blow off pipe.
All radiators are hot and bleed

Thanks in advance

Kev
sometimes when a boiler lights and the pump starts the pressure will drop because the gauge is on the return pipe and as such is on the suction side of the pump, but if you have to top up then there is another problem, what is the system pressure when the system is cold before start up and then when it is hot.???

Mog
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Old 17 October 2004, 23:22   #3
easyrider
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Could possably be an inline filter in the return thats starting to block up which can cause an excessive pressure differential when the pump runs.
The B.Gas insurance is a good idea for combi's due to the pain/expense of the fault when they go wrong.

Gary
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Old 17 October 2004, 23:49   #4
gsm1
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Don't be too concerned with the pressure drop when the heating starts but if you are losing pressure and having to refil then I'd strongly suspect a leak somewhere in the piping or a faulty pressure release valve (prv). There are other possibilities but considering it's quite new I wouldn't think them to be an issue.

Fill it up to 3 bar and check the prv exit pipe for water. If it leaks then just turn the prv **** a few times to try and reseat it.

Otherwise check for leaks on the ground floor piping.
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Old 18 October 2004, 00:11   #5
easyrider
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Sorry-didnt read the post properly-youre definately leaking somewhere.After you top the pressure up,turn the heating on and keep an eye on the gauge,if the pressure rises up fairly quickly to 2.5/3bar,then the chances are that the expansion vessel needs repressurising/replacing.If the pressure only slowly rises and doesnt go much above 2 bar when at max temperature,then the vessel should be o.k-check outside to make sure the o.flow isnt discharging-if it is,then its best to get a new pressure relief valve-if it isnt discharging,then look for leaks elsewhere-rad valves are usually a favourite place to start.

Gary.
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Old 18 October 2004, 10:07   #6
Buzzer
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Quote:
1. The boiler is steadily losing pressure requiring a top up every 3-4 days from 0.5bar to 1.5bar.
Thats a leak As said pump the pressure up and check all your valves. If its not that then start taking up floorboards

We had a consistent leak for years and we only found out when we changed from a back boiler to a combi and a pressure test was performed. It was underneath the floorboards in a bedroom. Luckily there was a few stray bits of plasterboard underneath it which soaked the water up.

Another tell tale sign is that you are continually having to bleed your rads
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Old 18 October 2004, 13:19   #7
Kev_turbo
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Thanks for the comments. I suspected there would be a leak somewhere just have to get under the floor to check it out. Luckily there is a matwell and it is possible to get into the foundations. Hope it isn't upstairs as the bathroom and office bothe have tiled floors.

As stated above there isn't any discharge from the PRV pipe and the rads have only been bled recently as another rad had been turned on, they don't need constant bleeding.

I will check under the ground floor tonight and report back.

Kev
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Old 19 October 2004, 23:39   #8
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Might also be worth checking your rads... they can rust.

John.
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Old 19 October 2004, 23:39
 
 
 
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