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Thread: Switched to evohome & caused damage to boiler?

  1. #1
    Automated Home Jr Member
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    Default Switched to evohome & caused damage to boiler?

    I have recently switched all my TRVs to HR92s; I also swapped out my hive relay/controller for a BDR91 and it was easy as that - evohomed!

    FYI, I have a Worcester Greenstar 30si, and I have decommissioned a Hive system (with dumb TRVs) to install the above kit. But the main radiator (which was in the same room as the hive thermostat, and didn't have a TRV) was almost always on, as long as any one of the other radiators was on.

    So: I thought I was being clever by adding a TRV valve to the main radiator (I did this by simply de-pressurising the system using a bleed valve, using pipe-freezing spray, etc.).

    However, I started to think about it, and I got worried... What happens if all the TRVs are off (at 0%), and (due to sync delay) the boiler is still providing/pumping to the CH? Is it pumping against a closed system? If so, can I damage my system?

    For now, I have put a TRV on a small radiator at set it to 5/5... But do I need to call a plumber and put in some plumbing to cope with the above scenario?

  2. #2
    Automated Home Guru
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    You need to have a bypass valve installed if you have HR92s on all the radiators. Do you have one?

  3. #3
    Automated Home Ninja Dan_Robinson's Avatar
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    Just leave the bathrooms uncontrolled.

    Or get a plumber in to fit an auto by-pass.
    Kind Regards - Dan Robinson (Jennings Heating Ltd)

  4. #4
    Automated Home Jr Member
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    Thanks for the advice.

    Quote Originally Posted by chrisgare View Post
    You need to have a bypass valve installed if you have HR92s on all the radiators. Do you have one?
    I thought so. I do not have a bypass valve installed (all I can see is a MagnaClean, and a silver cricket-ball-sized thing which I assume is some sort of expansion vessel).

    Quote Originally Posted by Dan_Robinson View Post
    Just leave the bathrooms uncontrolled. Or get a plumber in to fit an auto by-pass.
    For now, I've left a radiator in the main room uncontrolled. But I want to put in an external thermometer, so I may get both done, along with the upcoming service.

  5. #5
    Automated Home Legend
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    Some boilers have internal bypass valves too. So check that

  6. #6
    Automated Home Jr Member
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    Apparently, it has got one! I guess this is why I didn't do any (apparent) damage.

    However, the manual says: The boiler is equipped with an internal bypass. The internal bypass is not intended to be a substitute for an external system bypass. An external automatic bypass should be used if the system flow can be significantly adjusted or stopped by zone valves and thermostatic radiator valves (TRV).

    I guess it'll pay to have an automatic bypass fitted so I don't end up needing a new boiler?

  7. #7
    Automated Home Ninja
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    Bear in mind that ABVs don't play well with pumps that adjust their pressure/flow rate based on the pressure in the system (proportional pumps).

  8. #8
    Automated Home Sr Member
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    IMO its better to have a bypass radiator.

    My system has an internal boiler bypass and an external auto-bypass, and still had issues. I now have the hall radiator as a bypass as well but low.

    The issue i found with an ABV was that when all radiators were off and the boiler still going for a short period the return temperature was no different to the flow temperature and the boiler didnt like this so shut down until a reset.
    I know have the bypass radiator so some heat can be dissipated the ABV still ensures a good flow but i use it mostly to keep the system quiet.

  9. #9
    Automated Home Jr Member
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    What is exactly is a bypass radiator? And how do you go about setting up a radiator to act as a bypass radiator?

  10. #10
    Automated Home Ninja
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    Quote Originally Posted by Karrimor View Post
    What is exactly is a bypass radiator? And how do you go about setting up a radiator to act as a bypass radiator?
    It's a radiator without a thermostatic valve on it, so it's always open. I use my towel rails, and just leave the lockshields closed right down, but not fully down.

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