Evohome - bypass issue?

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  • joolscog
    Automated Home Lurker
    • Apr 2016
    • 4

    Evohome - bypass issue?

    Hi,

    I'm hoping that someone can give me some reassurance that my Evohome config has suitable bypass.

    Recently had an Evohome system installed in what I believe is an S-plan config (a single 2-way valve controlling flow to the hot water only, flow is "always open" to the radiators). I have a boiler and DHW relay fitted and HR92s on all the radiators. Based on those parts of the system I can get access to, I think the house plumbing and Evohome installation is configured as in the image below.

    MyPlumbing-EvoHome-Diagram.jpg

    I have been keeping an eye on the timings of HR92 opening/closing, when the boiler, boiler relay and water pump turn on and off. From what I have observed, the sequence is as follows:
    - HR92 opens, Boiler relay on/boiler on, pump on, HR92 closes, boiler relay off/boiler off, and finally pump off (a minute or two later). As the pump appears to stay running for a period after the HR92 has closed I wanted to check if I've anything to worry about!

    I'm no expert, but there appears to be a by-pass circuit immediately above the boiler - see photo below - so I believe that this should be sufficient?

    BoilerPiping-sml.jpg

    Before Evohome, none of the rads had TRVs (all were manual valves). At the moment, I have removed the HR92 from the bathroom radiator and manual left the valve "half open" to ensure that I have sufficient by-pass circuit whilst I clarify if I have an issue with the current config.

    Can anyone confirm that bypass is sufficient given the configuration - and so I can happily re-fit the HR92 to the bathroom radiator without anything to worry about! Or is there something I need to check?

    For info, I have a Potterton Suprima 70L boiler.

    Thanks, J.
  • top brake
    Automated Home Legend
    • Feb 2015
    • 837

    #2
    Does look like a fixed bypass. Best to install an automatic bypass to stop waste. Pop the HR92 on and see if the system works and isn't too noisy. Only way to tell is try.
    I work for Resideo, posts are personal and my own views.

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    • DBMandrake
      Automated Home Legend
      • Sep 2014
      • 2361

      #3
      Just be aware that if there isn't any bypass at all then the pressure build up when all radiators close and the pump is still running could cause some marginal joints in the pipework to start to weep - we had this issue in a rented flat where the bathroom radiator joints would start to leak if all radiators were closing. It can also put a lot of unnecessary strain on the pump, shortening its life.

      Personally for peace of mind I would get a plumber in to fit an automatic bypass valve - even if you do have a conventional bypass (just a slightly open valve) the ABV is far superior and will lead to less energy waste and a happier running system and the ability to control all radiators without issue. An ABV will not open at all when multiple radiators are open thus there is no waste in this state, however as radiators close down then by the time you have about one radiator open the ABV will start flowing and act to regulate the differential pressure between flow and return to the set value, which can also help reduce radiator noise when only one or two radiators are on.

      When I had a plumber in doing work on the system when we first moved in to our current house I asked him to fit an ABV well in advance of installing Evohome myself some 6 months later and I'm glad I did, as the elimination of an always on bypass radiator is a big benefit of a fully zoned system IMHO.

      An ABV is not expensive by the way, a good one can be had for under £20, so it's really just the labour of fitting. Depending on your system you may need a partial or full drain down to install it though.
      Last edited by DBMandrake; 31 May 2016, 11:42 AM.

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