Mainsflow Thermal Store problem - Coil failed?

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Hi,
I installed an Albion Mainsflow thermal store about 5 years ago. It's this type here to save explaining how it works:
http://www.albionwaterheaters.com/pdfs/sales/mainsflow.pdf
It's the direct contractor version on page 3 where the store has a float valve at the top and acts as the feed and expansion tank for the boiler/radiators as well as providing hot water.
The problem is its been overflowing (about half a bucket per day). It's not the float valve as I've cut and capped the pipe going to it, so that only leaves the DHW coil. I connected a pressure tester to the coil and didn't get any bubbles or noticeable drop in pressure, but there's no other way for water to get into the store.
So I'm left with two options. Either replace the coil with an external plate heat exchanger, pump and flow switch. This'll cost about £250 in parts to do. The downside is if the copper coil is failing, will the cylinder itself go in time? If so, it might be better to replace the whole thing, maybe going for a more conventional unvented cylinder, which are pretty cheap (e.g. Vaillant Unistor 155 is less than £600 + fitting). I could also switch to a sealed system for the boiler/rads. But unvented cylinders aren't DIY (how much would a pro charge do you think to put one in?).
Any advice appreciated.
Cheers, Antony.
BTW I've posted the same question on a couple of other forums if you should happen to see it posted....
 
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Sounds to me like your boiler stat may have failed and is bubbling over, or as you say the primary coil has gone. Can you isolate the coil and re- test or pressure test the coil?

HTH Gareth
 
Sounds to me like your boiler stat may have failed and is bubbling over, or as you say the primary coil has gone. Can you isolate the coil and re- test or pressure test the coil?

HTH Gareth

Thanks for replying Gareth.

I'm certain the boiler is OK. The temperature of the store is fine. When you take the lid off the store the water is dark green (copper perhaps?) but it's been well treated with Sentinel X100.

I isolated the DHW coil in the store (remember the content of the coil is fresh water at mains pressure, the store contains the primary fluid going around the boiler and rads) and used a Rothenberger pressure tester and my bike track pump to put 4 bar air/water in the coil. It held the pressure OK for several hours. I'd expected to see bubbles when looking into the store, but saw nothing.

Assuming the coil is leaking, it should only be going one way as the content of the coil is about 3 bar higher pressure than the content of the store. So the tap water shouldn't be contaminated. Even so, I don't like the idea of the water mixing...

Cheers, Antony.
 
Yes I know that the store is primary stored water lol. I an an istaller not a diyer.

The only way the header can over flow is ball cock. Split/damaged coil or boiler stat. Forget about looking for air/ testing with air. You may never see bubbles as they could accumulate under the header itself. Get your self a pressure gauge mate and pressurise the coil with mains water. Leave for say 4 hrs and look for a pressure drop.

Hth
 
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Yes I know that the store is primary stored water lol. I an an istaller not a diyer.
No offence intended. These aren't that common a design (though there are a few about), so I wanted to clarify.

The only way the header can over flow is ball cock. Split/damaged coil or boiler stat. Forget about looking for air/ testing with air. You may never see bubbles as they could accumulate under the header itself. Get your self a pressure gauge mate and pressurise the coil with mains water. Leave for say 4 hrs and look for a pressure drop.

Hth
There isn't a separate header. The float valve sits in the top of the store itself. This failed a while ago (the heat damaged the plastic of the valve, so a bit of a design fault), so I cut and capped the pipe supplying the float valve. So there's no way water can get in that way.

Cheers, Antony.
 
no problem bud. In that case then i would imagine that you should see bubbles of some sort. However if it is a minute pin hole then maybe not.

How long does it take to over flow from say 3" below the overflow? Narrowed it down to 2 of 3 possible faults now..
 
no problem bud. In that case then i would imagine that you should see bubbles of some sort. However if it is a minute pin hole then maybe not.

How long does it take to over flow from say 3" below the overflow? Narrowed it down to 2 of 3 possible faults now..

I get about 5 litres of (dark green but otherwise clean) liquid a day (I'm collecting in a bucket).

Cheers, Antony.
 
5 litres per day isnt a lot matey so maybe you wont notice notice testing with air. Test with water and a guage over say 4-5 hrs
 
The coil might only be leaking when the store is up to temp, try pressurising the coil when the store is hot.
 
It is VERY likely that the HW Coil has failed these units are utter C**p we have a client that has had THREE in Five Years all have suffered hot water coil failurte resulting in an overflow from the header tank I would consider converting to a Sealed heating system and UNVENTED hot Water :rolleyes:
 

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