Mainsflow Thermal Store problem - Coil failed?

Discussion in 'Plumbers' Talk' started by Ajones, Nov 6, 2010.

  1. Ajones

    Ajones New Member

    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.
     
  2. doing a bit

    doing a bit New Member

    firstly do you have a prv fitted on the cold mains supply to the coil in the cylinder ?? this is a common problem on this type of unit, overpressure will cause premature failure. if the coil has failed it doesn't mean the actual cylinder will be failing, constant heating and cooling of the coil causes it to be brittle, this coupled with overpressure can cause pinholes. look at repairing the coil if its a pinhole and fit a prv too.
     
  3. Ajones

    Ajones New Member

    Thanks for the reply.
    Yes there is a PRV. The thermal store came with one, and I installed it just after the incoming main stop tap. It's set to 3 bar.

    How practical would it be to repair a pin hole (or holes) and if I do, isn't it likely there are other places that are about to go too? Or is this type of failure highly localised?

    I chose this type of system hoping its simplicity would make it low maintenance and reliable over the long term. So if I've got to do some work, I want to be sure it'll last a good few years before I have to touch it again.

    Cheers,
    Antony.
     
  4. Water Systems

    Water Systems New Member

    <ol>[*]I would fit a plate heat exchanger, pump, check valve after the pump & flow switch. Then the PRV can be taken off, as most plates operate up to 10 bar. This will outperform the existing Mainsflows coil, giving hot water a few minutes after startup from cold, as it takes the hot water from the top of the cylinder.

    [*]If you know where the pin hole is, you can clean up the copper around the hole, tin it with solder, cut out a piece of copper, tin that on one side placing it over the hole and solder in place.

    [*]Do not go for a conventional cylinder & tank. Once you have experienced instant hot water at mains pressures everything else is retro and let down.</ol>
    If you are to replace the whole unit, then try Advance Appliances Thermal Store which is stainless steel.
    http://www.advanceappliances.co.uk/gas_or_oil_thermal_storesystems.html

    [​IMG]
    They will do custom made units as well.

    I know of Mainsflows that have been in for aprox' 15 years with no trouble at all. The owners speak highly of them.

    <ol>[*] You have a "direct" thermal store. Ensure you have enough inhibitor in the unit. About 3 cans.[*] Fit a Fernox TF1 filter on the radiator return to the cylinder. This is essential.  http://www.screwfix.com/prods/84311/Plumbing/Central-Heating-Treatment/Fernox-TF1-Total-Filter-22mm</ol>
     
  5. HOTDOG ø

    HOTDOG ø Active Member

    15 years is about the limit for a Mainflow walter ;)
     
  6. Water Systems

    Water Systems New Member

    You made that up.

    Advance Appliances stainless steel thermal stores will last and last and last. :)

    - Walter knows these things. You do not.
     
  7. Captain Leaky

    Captain Leaky New Member

  8. imran_

    imran_ New Member

    When one person "knows" something and no-one else does, it's usually because THEY have made it up....
     
  9. Captain Leaky

    Captain Leaky New Member

    What!

    Walter making things up?

    Never ! :)
     
  10. Water Systems

    Water Systems New Member

    When one person "knows" something and no-one else
    does, it's usually because THEY have made it up....


    Im-walked, I totally agree!
     
  11. Water Systems

    Water Systems New Member

    Keep on topic. If you have nothing to add to the topic do not post.
     
  12. doing a bit

    doing a bit New Member

    Antony.

    what size is the coil ? diameter ? could you fit a new coil ( original manufacturers) or make one with coiled copper pipe, should last a while , might save you a bit of money
     
  13. Captain Leaky

    Captain Leaky New Member

  14. Water Systems

    Water Systems New Member

    If you know where the pin hole is, it may be worth cutting out the section of the coil and replacing with a small piece of pipe preferably brazed in.

    But if one part has failed them maybe another section would in a year or so time. Best read my post above.
     
  15. Captain Leaky

    Captain Leaky New Member

  16. Water Systems

    Water Systems New Member

    nutcracker is the company that did the web site. Duh!
     
  17. Captain Leaky

    Captain Leaky New Member

    Yeah, but how appropriate! :^O
     
  18. Ajones

    Ajones New Member

    "doing a bit":

    The coil is made of 4 10mm pipes. It goes round the cylinder about 10 times. See these photos I took last time I drained down the cylinder a couple of years ago:
    http://img709.imageshack.us/img709/2900/p1130267.jpg and http://img3.imageshack.us/img3/1084/p1130262k.jpg

    It's sod's law that if I find the leak(s) they'll be in the hardest part to get to. If I had to put money on where it is, I'd bet it's where the pipes are soldered into the end-feed manifolds - there must be a fair bit of thermal stress there.

    I guess I could just replace it with a new one made out of microbore tube, but it'd be a lot of hassle. I think it'd be quicker to cut it out and install an external plate heat exchanger. I'm waiting for a call back from DPS to quote for a GEA Ecobraze and a flow sensor. But if their price is too high, I might take up your idea.

    Or just rip it out and put in a cheap unvented cylinder - at least they give a 25 year guarantee, 24 years longer than Albion. :(
     
  19. Water Systems

    Water Systems New Member

    • Go for an Advance Appliances stainless steel thermal store. [*]Remember you have a wonderful CH buffer there as well. Do not underestimate that. Keep it. 


    <ol><ol>[*]It eliminates inefficient boiler cycling. [*]Means a cheaper, simpler boiler can be used[*]Boiler last far longer, as it only burns for a few times per day for one long efficient burn. [*]The boiler is operating in the ideal hydraulic environment.[*]A smaller boiler can be used.</ol></ol>
    Farnell will do the flow switch cheaper.

    Below: the flowswitch - no moving parts:
    http://uk.farnell.com/productimages/farnell/standard/42421130.jpg

    Farnell will supply the flow switch, the FS05
    http://www.farnell.co.uk Farnell number: 1006771 with 22mm compression joints. Check the model, FS05.

    Flow Switch, makers site: The FS05 240v model.
    http://www.gentechsensors.com/productTemplate.asp?ProdId=113

    This flow switch is about the best - very good.

    Gledhill will supply a Plate Heat X. Or search on the web. The model for the 125 litre Systemate will do. Price up.
     
  20. doing a bit

    doing a bit New Member

    could you do a air pressure test to find the leaky pipe ? judging by the cost of 10mm copper pipe now it would cost a few quid to replace it !! the idea with the plate and pump means more parts and pump noise ! unventeds are good assuming you have the correct pressure and flow rates ( assuming it works well now) then that would be my choice, BUT you will need a expansion tank or expansion vessel depending on your boiler, more cost and work. No good news really, try the air pressure test first, good luck
     

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