Boiler pressure drops but no adverse effects.

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10 Dec 2005
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Location
Leeds
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United Kingdom
Hello,

I noticed last week that the pressure on my combi was at zero.

I topped it up and left it.

This morning I noticed it at zero again, so I topped it up.

This afternoon its on zero, which makes me think its been on zero for some time.

The strange thing is, the thing seems to operate just fine, plenty of hot water and heat.

Should I be concerned?[/b]
 
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Best get it sorted, not a good idea to keep topping it up. Probably just enough pressure to keep the boiler going.
 
you've either got a leak or a busted expansion vessel.

refill to your 1 / 1.5 bar, leave the heating & hot water off (give it an hour), if it steadily declines while cold then you've got a leak somewhere, fix this first!

if it stays put, get the heating on , keep an eye on the pressure,
if it goes up to about 2.5 / 3 bar then the boilers expansion vessel will need recharging or replacing.
(the excess pressure will be let off by the pressure relief valve, and you should have water exiting the building, normally a copper run outside that could be tee'd into the wall)
 
you've either got a leak or a busted expansion vessel.

refill to your 1 / 1.5 bar, leave the heating & hot water off (give it an hour), if it steadily declines while cold then you've got a leak somewhere, fix this first!

if it stays put, get the heating on , keep an eye on the pressure,
if it goes up to about 2.5 / 3 bar then the boilers expansion vessel will need recharging or replacing.
(the excess pressure will be let off by the pressure relief valve, and you should have water exiting the building, normally a copper run outside that could be tee'd into the wall)


Thanks very much for this.

I did notice the pressure on 3 bar today when the heating was on.

I'll try your procedure tomorrow and let you know.
 
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I followed the above procedure,

Went up to 3 bar with heating on with water dripping from the copper pipe outside.

So i'm looking to recharge my expansion vessel?
 
As a general test, if the air inlet valve on the EV sprays water when you press it (car schrader valve type) the EV is goosed.
With the boiler pressure at zero, pump air into the EV to around 10 psi or whatever the manual says. Its a good idea to disconnect the flexible water pipe to the EV when you do this.
When reconnected, use the filling loop to bring the boiler pressure up to about 1 bar - turn the heating on, and the pressure should rise to 1 1/3 bar, and then back down again with the heating off.
John :)
 
Yes and make sure there is no water in the vessel.
A vessel half full with water having the correct pressure 0.8bar still can't do what's it's supposed to do.
You'll may also find after fixing the vessel problem that the PRV does not seal properly and that also needs replacing or cleaning (if you can get it apart)
 
ok,

If the boiler carries on giving out heat and hot water, do i need replace the vessel (if its broken)?
 
Yes for two reasons really - its a safety device as yours is a sealed system, and you don't want to be introducing fresh water at all - it will start corrosion.
John :)
 

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