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Thread: Converting Evohome Y-plan to use OpenTherm

  1. #1
    Automated Home Jr Member
    Join Date
    Jan 2021

    Default Converting Evohome Y-plan to use OpenTherm

    We have Evohome working with a Y-plan system, with an old vented hot water cylinder and an old boiler on an open vented heating system. There are two BDR91's in the airing cupboard, one that calls for hot water, and one that calls for heat. There are HR92 radiator controllers, and there is an automatic bypass valve. The cable to the boiler is wired to allow for pump overrun.

    We are planning to get an Intergas HRE OV boiler and the Evohome OpenTherm Bridge.

    Am I right in thinking that the above set up remains the same with the new boiler (including the cable to the boiler to power on the boiler, and in turn allow the boiler to power the pump) - the only difference is adding the OpenTherm Bridge to the new boiler?

    I've read that there are ways of altering the wiring to allow for Priority Domestic Hot Water - but I presume that the new Evohome firmware will now do this with software?

    Replacing the vented hot water cylinder with a new rapid recovery vented hot water cylinder will allow faster recovery of the hot water cylinder (while heating is temporarily suspended).

    Assuming I've understood all of the above correctly - will Evohome via OpenTherm automatically adjust boiler temperature when calling for heating vs hot water? ie. the OpenTherm Bridge operates in parallel to the existing wiring to simply adjust boiler temperatures?

    I realise I may have completely misunderstood how the OpenTherm Bridge is to be installed - the documentation seems to be severely lacking (hence why I'm making the assumptions above, otherwise I would expect separate wiring diagrams for when OpenTherm is being used).

    PS. I'm not planning to install the boiler myself, I'm hoping to find someone that knows what they're doing - I simply want to understand it myself to make sure the installer is doing it correctly! (I did install the current wiring myself, so I do understand the current set up!).

    PPS. I've been suggested getting the eco RF instead without connecting it to hot water, so using heat only function - but am I right in thinking this would mean converting to an pressurised sealed system (eliminating the expansion tank in the loft?).

  2. #2
    Automated Home Legend
    Join Date
    Jan 2015
    NE UK


    I am in a similar position. My boiler more and more produces greater noise like a dying pair of lungs. I am looking at Intergas but an Intergas system boiler. This gets rid of tanks in my loft and gives hot water at mains pressure. My shower pump can go. A thermal store is worth a thought. Hot water is heated as it comes from the rising main. It gives a degree of future proofing as the cost/and type of power may change in years to come. They are not cheap. A vented tank is simpler and requires less maintenance and an unvented one requires the installer to be properly qualified and to be serviced regularly (the tank not the engineer!). Not done properly and the tank can take off through your roof like a rocket taking off at NASA!. Opentherm I don’t have at present, well not with my old boiler, but is sensible. There are others here with a lot of expertise on such but generally it helps the boiler work more efficiently.

    If not getting a combination boiler don’t over spec what you need. 12kW or 18kW may be more than adequate, more efficient and cheaper than being persuaded to be install a big boy whose power you will never need but I believe wears out more quickly. Also you may need to replace radiators depending on their age.

    For a long time the Intergas site did not produce an approved installer near me and I have found a number of central heating so called “experts” seem to have no real knowledge of Intergas but feel free to criticise them. Independent experts think otherwise! Recently their site came up with an approved installer 13 miles from me.

    You might find this site helpful:

    You read they recommend Intergas.

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