Hi all
One of my colleagues is struggling with a combi system.
Problems are:
Whistling boiler when CH or hot water calls for heat. Total loss of pressure when boiler isn't running - returns to 1 bar when boiler operational.
My knowledge of heating systems is limited to open-vented so any ideas appreciated.
TIA
Phil
Kettling perhaps? (Caused by system pressure being too low amongst other things).
Tim
I would consider that it has no pressure - but when it gets hot it causes some pressurisation.
Go to the good old FAQ and learn to bleed and pressurise the system.
John
"John" wrote
I gave him a copy of the FAQ and he claims to have followed the procedure for bleeding. Not sure if he has added inhibitor though! Would the lack of inhibitor allow sufficient build up of compressible gas to lose the initial 1.5 Bar charge?
Phil
Could be the classic failure of the expansion bottle problem. Boiler runs, water expands, pressure rises above the pressure relief valve limit and it blows off the excess pressure. When the system cools the pressure in effect falls to zero. Bleeding all the rads would make this worse rather than better.
"John Rumm"wrote
John
Do I understand this right? The diaphragm splits/holes, and when you bleed the system and fill it up completely, you also fill the "air side" of the diaphragm in the expansion vessel. So when the boiler fires up, the pressure increases and relieves straight away due to no expansion room.
How is it best to test this? Pardon my ignorance, I have vented system myself.
Put a plastic bag over relief valve outlet? Anything else like watching pressure?
Thanks
Phil
1) Put water in and bleed system of air to get a pressure of about 1.0 bar cold. 2) Switch heating on and watch the pressure rise excessively and/or throw water out the discharge pipe. 3) Observe pressure reduction to near zero after switching off heating.
Will need a new expansion vessel (repressuring may work but usually doesn't fix it for more than a short while [1]) , maybe a new pressure relief valve, maybe clearing out corrosion debris.
[1] Whatever caused the dry side pressure collapse will still exist.
Yup, spot on.
Yup.
Yup.
To fix it you have a few options:
You could try pumping up the pressure vessel (it will have a car tyre like valve on it), however if it is knackered rather than just deflated this won't help.
You could either replace it (can be tricky) or just add another one somewhere else in the system.
If you need a quick fix bodge to keep things running you could half empty a radiator so it has a big pocket of air in it. This will then act as a pressure vessel for a bit.
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