Unvented cylinder constantly discharging

Solidair11

Hello,

I've got an indirect unvented stainless steel hot water cylinder (Albion 150l, Danfoss thermostat box on the outside) with an expansion vessel. The heating seemed to be working fine as far as we could tell but it turns out this cylinder has been constantly discharging water to the back garden under gravel for goodness knows how long (at the rate of roughly 1.5 litre per half hour).

A suggestion was made that it might be a stuck valve or the thermostat being broken causing it to permanently heat up and then vent the water, cool down and repeat the cycle.

Does anyone have any pointers for me to to better establish the true cause or recommend a good book on the subject just to understand more myself before getting the contractor to do the suggested repair? (A quote I've had seems to suggest replacing 4 parts at £600, the logic being that one part fails then the others often follow).

Thanks in advance for any recommendations!

nofoollikeold

1. There are two likely points for water loss:
1a. The combination valve on the cold water inlet.
1b. The temperature and pressure relief valve on the cylinder itself.
2. Both these valves should be connected to something called a tun dish. This has a small pipe coming in at the top, and a large pipe going out at the bottom. Between top and bottom there will be a gap where you should be able to see water flowing through (if there is any). There is usually only one tun dish fitted with both valve connected to the top (inlet).
3. If you can see water flowing through the tun dish, one of these valve will be the source of the leak.
4. If the leak is continuous, and the water is cold, its most likely coming from the inlet combination valve.
5. If the leak only occurs when the water is hot, and the leaking water is itself warm to hot, then it is most likely the temperature and pressure relief valve.

However, any work on the cylinder or its attachments must be undertaken by an engineer who is "G3" qualified. The cylinders are potentially dangerous and require special training for anyone working on them.

Also, you need to be certain the leak is from the cylinder. Have you checked the pressure relief pipe from your boiler?

Solidair11

Thanks alot! I can visually see the pipe that's discharging water coming directly from the cylinder, not sure if that totally answers your last question at the end. I haven't checked pressure relief pipe and am not sure how to do that (or if I should given the G3 status) but will try and read up more online.

I'll check these other points this weekend too! Besides the continues discharging externally, there's also occasional leaking around the boiler pipes (enough to fill a sweetie tin). I was previously told all this was normal behaviour.

I'm not going to attempt the repair work myself but I just wanted to better understand how the system all fits together and works (It was there before we moved in). We've had several other expenses for rot and things since moving in, so I'm trying to at least get clued up a bit better myself as I know I've received bad advice before.

Does the repair cost of £600 for four new parts seem reasonable? I'm in Scotland. (ie not London prices)

Thanks again!

Owain_Moneysaver

Parts:
cold water combination (expansion relief and pressure reducing) valve about £40
temp & pressure relief valve about £20
cylinder thermostat (boiler control) about £20
unvented cylinder expansion vessel about £40-60

If those are the parts he's replacing, total about £120 or so. £480 for labour - 5 hours at £100 an hour - sounds highish to me. Depends where in Scotland though. Edinburgh isn't cheap, neither are the Highlands and Islands for skilled labour.

You haven't left the immersion heater on have you? Worth checking.

http://wiki.diyfaq.org.uk/index.php/Unvented_DHW

Solidair11

Thanks again, so helpful! I'm bookmarking that site too, it's clearer than alot of the online explanations.

I'm near Edinburgh so guess prices are the same as there.

Is there an easy way to tell if the immersion is left on? It's not something I've ever controlled, I just use the main house temperature thermostat normally and was oblivious to all of the other bits until very recently Unfortunately there weren't any manuals or anything in the house. (Have googled for that but it looks like the latest versions are a bit different, I can't find the same kit). Cheers again!

Owain_Moneysaver

Solidair11 wrote: »

Is there an easy way to tell if the immersion is left on?

There may be an indicator light on the switch
The casing may feel warm
Your electricity meter will be galloping along

Solidair11

Thanks again for all these tips. I had a look at the pipes at the connections for the Tun dish and saw a couple of candidates but there doesn’t seem to be any connector that has a visible area to allow me to view the flow of water, unless it’s so obscured in where it is I just can’t see it.

The thermostat was cold, it doesn’t have a light or any indicator, though rummaging further made me see it has a separate electric cable running from a power switch behind. The power switch was now turned off though that may have only occurred recently after the initial contractor took a look at it.

Our electricity bill always seems high but it’s a big old house and this could have been happening since we moved in so hard to say if it’s galloping along.

The externally discharging water is warm-ish but not hot either (but not mains cold).

Cheers again for all the pointers, I think I’ve exhausted the limits of what I can check and at least feel better informed. (Looking at like for like parts alone they seem to add to only about half of the £250 I was quoted for that so presumably they’re all marked up for extra margin.)

I think whatever happens I might see if I can upgrade the thermostat to something wireless so I can keep an eye on it for any unusual future activity changes.

Cheers again!

Solidair11

Hello again,

Just wanted to post an update on the outcome of this...

I found another heating engineer through a colleague in work for a second opinion, they came and looked at it. (turns out my system doesn't have a tun dish on it he showed me where it would normally be).

He checked the expansion, etc. and reckoned it was worth changing the valve (£16 for the part), the leak stopped immediately and has not returned. No other parts needed replacing (they thought the suggestion that others would very likely fail wasn't necessarily true).

In the end it cost me £60 and was done in just over an hour. So glad I didn't spend the £600 pounds and replace 4 (heavily marked up) parts the other firm were suggesting was necessary.

Thanks again for everyone's input!