Heating coil leaking in hot-water cylinder ?

Seamus Farrell

Folks,
This is my first post here.
I have a strange problem, probably similar to one already described in this forum, but I think I have some additional information that might pin-point the cause.

Here's what I've observed :
- There's a constant trickle from the overflow coming from the main cold-water tank in the attic - about enough to fill a bucket in an hour.
- The small central-heating cold-water reservior tank, located above the main cold water tank in the attic, is constantly filling at about the same rate as the overflow, but doesn't itself overflow.
- The cold water in taps supplied from the attic tank is warm.
- The water in the hot taps is a bit discoloured.
- The immersion heater has not been on, and the hot water, heated by the central heating, is no hotter than normal.
- There are no obvious leaks in radiators or pipes that could account for the constant filling of the central heating reservior tank.
- The ball-cocks on both cold water tanks close properly when the lever is lifted.

Tried the following :
- Closed valve on pipe supplying cold water from main attic tank to hot water cylinder.
After a few minutes, the central heating reservior tank stops filling.
- turn on a hot tap (bath)
After a couple of seconds of normal flow, the flow slows down to a trickle (about the same rate as the overflow pipe), and the central heating reservior tank starts filling again (also at about the same rate)

This looks to me as if somehow the coil from the central heating system inside the hotwater cylinder is leaking, allowing water from the central heating to mix with the hot water in the cylinder. Because the central heating reservior tank is higher than the main cold water tank, hot water is being pushed from the cylinder up into the attic tank, via the cold-water feed, causing it to overflow and also warming the water in that tank.

If I'm right, I'm guessing that I'll have to replace the hot water cylinder. The house was built about 18 years ago. It's an old-fashioned version without "built-in" lagging.

Is replacing the cylinder beyond the capabilty of a reasonably experienced amateur?
I'm fairly good at DIY, and have done bits and pieces of plumbing (e.g. new shower with pump) without any disasters, and have replaced a faulty immersion heater, but this seems a bit more ambitious.
I expect hot-water cylenders come in standard sizes, but are the positions of the various plumbing connections also standard? Would it be better (assuming there's room) to fit one of the more modern lagged types?

To those who have read this far, thanks for your parience.

Any advice would be appreciated.

DublinDilbert

It sounds like you've identified the fault spot on. Not beyond a competent DIYer at all.

You'll need to drain the heating system and knock off the water going into the bottom of the coper cylinder. If there's no drain fitted on the bottom pipe coming form the old cylinder, you'll need to empty it, the easiest way would be to remove the existing immersion element and syphon the water into the bath.

Try get roughly the same size tank, will make your job much easier. Get a new immersion element while your at it. You'll need an immersion box spanner wrench to install it, if the new tank is insulated.

If your not comfortable with the electrics get someone who is to attach the new immersion wiring.

Seamus Farrell

Thanks DublinDilbert for the reply. I had to replace the immersion heater a year or so ago, because it stopped working. It was very corroded when I took it out. I got the required spanner, and with a bit of help from someone more expert than myself was able to change it with safety (isolate circuit and so on).

Thanks for the tip about getting the same size as the existing cylinder and about siphoning out the water from the top. I had been wondering how to drain it without making a mess.

bunglemark2

Folks

I started a similar thread here.
I'm wondering if I possibly have the same problem i.e. could the coil in the tank be leaking ? Would this explain the loss of pressure in the heating system ?
Any ideas what a new tank is likely to cost, even ballpark estimates ?

Thanks

Seamus Farrell

Just to round off this thread and report results:
I did manage to replace the hot-water cylinder (cost €150 inc Vat.) and all of the symptoms I reported in my first post have gone away.
Mind you, it took me all day to do it, and more complicated than I expected - isn't everything ? There was a total of 12 (!!) connections to open and re-do, none of which leaked (thank you lord).

To anyone with the same problem thinking of fixing it themselves, here's a couple of extra tips based on my (new) experience, to go along with the sensible advise offered by Dublin Dilbert:

- To the extent that you have room to see within the confines of your hotpress, measure and mark the angles / positions on the old cylinder of any right-angled plumbing joints directly attached to it. My space was confined (probably typical), so I had to take out the old cylinder and put in the new cylinder with 2 lengths of pipes attached to it. Marking everything saved several iterations of wrestling the new cylinder into and back out of the press to get the positions right. Also trying to adjust connections in situ runs the risk that a loosened joint will leak sometime later.
- I had to borrow an open-ended spanner with a right-angle on the end to open and later tighten the compression nuts on two of the connections. I'm not sure what that kind of spanner is called, but without it I couldn't have managed within the confined space. I intend to buy one for any future plumbing jobs.
- The positions of the connectors on the old cylinder were almost but not quite the same as on the new one and I had to change the lengths of some of the pipework. So, when you get the old cylinder out, stand it up beside the new one and make sure everything lines up. Then do any pipework adjustments before attempting to fit the new cylinder in place.

Would I have done the job myself had I known what I was in for? Definitely! :cool:

Micky Dolenz

Well done,
changing a cylinder can get tricky and experence comes into play.

A good plumber will change a cylinder in 3 or 4 hours, refilling system is often the slowest part. Doing it in a day as a novice is very impressive.

Seamus Farrell

Thanks Mickey. As may be obvious, I'm delighted, as much by the correct diagnosis as the completion of the job. Imagine if I'd been wrong ...
Any idea what that mysterious right-angled open spanner is called ? I've been browsing the web trying to find out amd so far without success.

Micky Dolenz

spud wrench?

Micky Dolenz

You did really well to recognise the symtoms, many plumbers would have missed them.

Seamus Farrell

I can't take the credit. It was a friend who came up with the suggested diagnosis, based on my description. After that, the result of turning off the stopcock connecting cold-water tank to hot-water cylinder seemed to prove it.
By the way, I found the name of the spanner. It's a tap-wrench or a basin-spanner. There's a picture of one at the bottom of this page.

LittleVision

Here's a puzzle some of you more expert may be familiar with. Since the cold weather when our header tank (outside on the roof!) was frozen we have had a change in how our hot water system works. We have a copper cylinder which is heated by a closed system from a solid fuel range (which also heats radiators activated by a thermostatically controlled pump) and also an immersion heater. One night during the freeze we left a hot tap running to keep all systems moving but our pump which takes water from a well died that night so the whole system drained. I got water back into the system by filling the header tank with buckets and after the thaw all resumed as normal ... EXCEPT ... now it takes ages, sometimes five minutes, to get hot water to the hot water tap, only a short distance from the tank, even when the tank feels very hot. Even once the hot water finally comes, if we turn off the tap for any length, we must then wait for ages again to get hot water again. The only conclusion I can come to is that whatever convection is going on in the tank, we must be getting water to our hot taps from the bottom of the tank first. Before the freeze we would get hot water within 30 seconds of turning on the tap. Anybody got any ideas why this might be happening and how it can be fixed? I would be much obliged for advice.