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Old 12-08-2022, 17:34   #1
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Can't drain the hot water cylinder water

I feel like an idiot but I can't seem to work out on my boat how to drain the hot water cylinder. If I close off the water tank">fresh water tank inlet lines to my water pump then I can't get any hot water through the taps. I've tried releasing the water through the short hose off the valve relief but it only let out about 500mls and then stopped. The cylinder is 40 litres. I've opened all the faucets to release pressure but barely anymore came out. I need to change the anode but need to drain it first to access it. Any ideas? Thank you! Pics attached of pump setup and cylinder setup in case it helps
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Old 12-08-2022, 19:13   #2
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Re: Can't drain the hot water cylinder water

Is there a top-mounted vent or pressure relief valve you can open to let air in while the water runs out? A way to bleed air from the tank that can be used to relieve the vacuum when draining?


If not, open hot water outlet and then remove cool water hose and blow air into the inlet into the tank to purge water. One of the tubes, hot or cold, probably goes higher inside the tank than the other.


If anode is higher up on the tank you might vent the air in there by loosening it.


You might be able to take the blue hose off the accumulator to blow air into the tank there.


Be sure to refill completely when done before turning on any heating elements! Bleed the air out!
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Old 12-08-2022, 20:07   #3
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Re: Can't drain the hot water cylinder water

I have one of these Sigmar hot water tanks. Mine is mounted horizontal and not vertical.
Anyway, on the cold water inlet there should be a pressure relief valve which also works as a drain valve. This black plastic valve lever can be pushed "down" for momentary drain, or lifted up to keep the valve open, while the water drains (usually via a hose) into the bilge.
If this valve does not exist on your system, this is a problem for 2 reasons... it makes it difficult to drain the tank; but more importantly the tank *may* get pressurised to more than it can safely handle and burst (explosively?).
As pointed out, refilling and getting rid of the air is critically important. The intake for the hot water outlet is a long solid pipe that runs inside for almost the entire length of the tank. Since your tank is vertical and all connections at the bottom (and therefore the hot water intake will be at the top) , you should achieve air free status very quickly.
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Old 12-08-2022, 20:13   #4
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Re: Can't drain the hot water cylinder water

I have just read your post again (sorry).
You are already opening the drain valve!
But because your tank is standing on its head, you are creating a vacuum. You will have to allow/force air into the hot water outlet, as the water drains out the drain valve on the cold water inlet
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Old 12-08-2022, 23:49   #5
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Thumbs up Re: Can't drain the hot water cylinder water

Thanks so much everyone for the replies. Just to clarify, the tank is on its side.

There's no long pipe along the side. There is a blue cold water intake down the bottom and hot water outlet half way up (see original pic). Ther are engine connections as well as it uses the engine heat.

I'm off the boat now as ran out of time but will test out some of your ideas next time and fingers crossed one of them works and I don't create a flood. I'm a bit worried though as none of the pipes are at the top and there is no release at the top, just the one at the bottom which doesn't seem to release much.

Cheers so much everyone and any further ideas before I head back out are very welcome! You're all amazing for helping!
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Old 13-08-2022, 01:18   #6
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Re: Can't drain the hot water cylinder water

OK, the tank is on its side (horizontal). The photos don't really show this. I presume (if the mounting feet are at the bottom) that means the hot water connection is at the top, which would put the cold water inlet (with the drain valve) at the bottom?
The intake tube for the hot water outlet runs almost the length of the tank, inside the tank and should be parallel with the top/sides.

I *know* this because I have just replaced my 60 litre tank with a brand new one at over $1000 because I couldn't get a usable amount of hot water from it. Once I got the new one and looked inside, then compared it to inside the old one, I could see that the old intake tube "drooped" towards the bottom of the tank. Everything above the low end of the intake tube was air only, and the volume of hot water less than litres only.
The attached photo shows a stainless rod inserted into the tube, to show the drooping angle.
Long story, but frustrating and largely unnecessary! Hopefully someone else can learn from thisClick image for larger version

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Old 13-08-2022, 01:33   #7
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Re: Can't drain the hot water cylinder water

That makes so much more sense now. Thank you! OK. So in that case I can hopefully release pressure by loosening the hour water outlet? Or maybe not because that will be into the bottom of the tank so may not release the air? At least that means I shouldn't flood anything by trying that top hot water outlet

Quote:
Originally Posted by Karanga View Post
OK, the tank is on its side (horizontal). The photos don't really show this. I presume (if the mounting feet are at the bottom) that means the hot water connection is at the top, which would put the cold water inlet (with the drain valve) at the bottom?
The intake tube for the hot water outlet runs almost the length of the tank, inside the tank and should be parallel with the top/sides.

I *know* this because I have just replaced my 60 litre tank with a brand new one at over $1000 because I couldn't get a usable amount of hot water from it. Once I got the new one and looked inside, then compared it to inside the old one, I could see that the old intake tube "drooped" towards the bottom of the tank. Everything above the low end of the intake tube was air only, and the volume of hot water less than litres only.
The attached photo shows a stainless rod inserted into the tube, to show the drooping angle.
Long story, but frustrating and largely unnecessary! Hopefully someone else can learn from thisAttachment 262760
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Old 03-09-2022, 15:50   #8
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Re: Can't drain the hot water cylinder water

Many thanks everyone for all the help. Finally got back to the boat yesterday and managed to release the pressure by opening the thermostat main bolt a bit. A little spillage but not too much so ended up being simpler that the other connections. Really appreciate all the help!
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