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My daughter who lives in an apartment in Melbourne sent me the following:
QUOTE
A question about hot water cylinders... I was reading the little writing on the side of ours, and it says there's a relief valve that should be relieved every 6 months. And it's under a larger heading called 'DANGER'. We haven't done this in all the 5 years we've been here. Then when I went to touch this relief valve it didn't seem like a lever at all. It was all free moving. I'm going to inquire about it when we have our next inspection, coz I think it will be due for it's 5 year check up, but my question is; do you ever release a pressure valve on your hot water cylinder?
UNQUOTE
I would say it's a fair bet the hot water pressure is mains supply and electrically heated.
I hope someone here can help her out, I've copied this link to her. Cheers.
The pressure relief valve is a safety valve, hence some valve manufacturers recommend you test the valve regularly to make sure it works. My recommendation is to get a yearly check (service) done, just to make sure the cylinder is operating efficiently and safely. One minimum charge a year towards the plumber could save you hundreds when you least expect it. Sorry for the late reply, better now than never aye.. 8)