Combi boiler pressure gauge question

[Kevinhardy2010]

Can someone please answer me this regarding a combi boiler: when the gauge reads 0 pressure (0 bar) on the dial, does this mean the boiler is empty or the system is empty up to boiler height/level? To be clearer what I mean is, if I want to drain water from my system to replace a faulty air bottle inside the boiler casing, how can I be sure water will not escape pour out when I remove the old 1!! The boiler is in our ground floor kitchen.

Thank you for helping.

 

[Burnerman]

It means that your system is full of standing water, without any extra pressure behind it...therefore work can be done on the system without fear of pressurised leaks. (Central heating side only).
With no pressure inside, breaking into the system will only mean the odd dribble of water, as the rest of the system is sealed.
John

 

[hammerswinger]

I would have to disagree with Burnerman on this.

If the gauge is reading 0 & you break into the central heating side of the boiler to remove the expansion vessel (air bottle) the water from any pipework / radiators above the boiler will flow.

To remove the expansion vessel you have to isolate the Central Heating circuit by closing the isolating valves on the flow & return pipes where they connect to the boiler. Then you will have to drain the water from the boiler, there will be a drain point(s) somewhere on the boiler to do this.
Only then will you be able to disconnect the expansion vessel. Be aware that there will be water in the EV so make sure to protect any electrical wiring / circuit boards etc that could get wet!

Make sure you have turned off the electricity supply to the boiler before doing any of the above.

 

[Burnerman]

Hey, we all have our own ideas and methods with these issues, but so long as a rad bleed valve isn't opened, you aren't going to get a flood as air can't get into the system.
Absolutely no disrespect with your way though!
I just depressurise and get cracking, and keep the system open for as little time as possible.
John

 

[hammerswinger]

Absolutely no disrespect with your way though!

Likewise with your method if it works for you.....

I appreciate the theory of your method.... if no air can get in no water will come out....but in my experience if things can go wrong they will so I like to err on the side of caution.

Cheers.

 

[Burnerman]

Absolutely no disrespect with your way though!

Likewise with your method if it works for you.....

I appreciate the theory of your method.... if no air can get in no water will come out....but in my experience if things can go wrong they will so I like to err on the side of caution.

Cheers.

No ones ever going to argue with that one, mate!
Cheers
John

 

[Kevinhardy2010]

Thank you both for your help with this query and your replies.

I have one further question though; I have heard that turning off the boiler valves to drain the boiler can often cause them to leak when re-opened. Is this very true or a myth?? If so is there anyway to stop the leak or any tips so they do not leak when closed and re-opened?

Thanks again, Kevin.

 

[dextrous]

It is true that these valves sometimes drip afterwards. No secret to it - just hope

 

[Agile]

Unfortunately the OP never said what kind of boiler he has!

Both of the two RGIs above would use the safest method appropriate to the actual installation.

John would isolate the boiler if it was in the basement of a three story house and particularly in the rads were old and leaking a bit.

Equally if it was a Potty Puma which has iso valves which start to leak even if you only look at them, Hammer would not move the iso valves either!

If you must replace an EXV yourself the its essential that you correctly set the air pressure ( see the FAQ on this sire ). They do NOT come set at the correct pressure! ( Unless you work for British Gas ).

Tony

 

[thefloosyonthebeach]

Unfortunately the OP never said what kind of boiler he has!

I hope its not a Worcester CDI