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Thread: EvoHome: do I need to leave a single radiator in my house without HR92 or TRV?

  1. #21
    Site Sponsor The EVOHOME Shop's Avatar
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    Quote Originally Posted by top brake View Post
    Very interesting

    Is this advice unique to WB?
    I am unsure if it is unique to WB but they obviously had issues with modulating pumps and S Plan at one point in time and this was their best solution.

  2. #22
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    Glad now that when having a new WB gas boiler and Evohome installed a few weeks ago that I left two small radiators and heated towel rail in the bathrooms without HR92's to keep down costs.

  3. #23
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    An open radiator could be a good thing, sure. Anyway, as I was saying before, my boiler gets loud when the embedded bypass kicks in, but the boiler itself shows there's a kind of overheating protection, so I don't think it could get damaged by overheating, because it just shuts the burner off and turns on fans and pumps to cool down the heat exchanger.

    I guess most modern boilers show similar behaviour, so there's no big risk - except for the noise effects.

    Yet I think my EvoHome is calling for heat when all valves are shut, thus hitting against the embedded bypass, and this, in my opinion, is a programming fault. If the EvoHome decides, based on the heating curve, that it's time to heat up some radiator, the procedure should be:
    1 - OPEN some valve
    2 - FIRE the boiler
    3 - When enough heat has been provided, STOP the boiler
    4 - WAIT a few minutes for the boiler overrun to finish
    5 - CLOSE the valve


    What I observe is different. Valves and boiler are driven independently, so sometimes the boiler is fired when all valves are actually shut. An open radiator or a spring-loaded bypass could take care of this but, computer-wise speaking... if you can fix it in software, what's the point of changing the hardware?
    Last edited by emmeesse68; 30th October 2015 at 09:51 AM.

  4. #24
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    Agree with emmeesse68. Is should be possible to make sure the boiler isn't fired anymore by the boiler-relay when all valves completed closing. And an extra safety margin of a minute or 2 to accomodate overrun should be built in as well.

    Monitoring the relay and hr92-valve behavior shows that it's not currently the case. Especially right after turning off heating for the entire house. The hr92s all close pretty quickly afterwards, but the boiler relay might fire again 1 more time a few minutes later.

    And then of course there's the seperate issue of HR92s fully closing water access to the radiator even when they're actually on 30% and shouldn't be closing it fully. I've seen this happening even on Honeywell-radiator-heads (V2000), both with the full-option on and off.
    Last edited by erik; 30th October 2015 at 08:39 AM.

  5. #25
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    Just to add my tuppence here as just been through this.

    I have a new W.B. Greenstar 30cdi (regular), Grundfos Alpha2L Pump (controlled by Boiler) and a Honeywell DU144 Automatic Bypass Valve (ABV).

    Firstly, an ABV is now a Building Regs requirement. Cannot use a manual gate valve to restrict flow.

    The Boiler, Pump and ABV all have to work as a team to make sure you have a small circulation loop for the boiler to lose heat at minimum flow rate, but not for the ABV to open too easily.

    The Grundfos has 3 operating modes: Fixed Speed (the standarard plumber I,II,III), Constant Pressure (CP1,CP2) and Proportional Pressure (PP1,PP2).

    The only ones that work with the W.B. and the ABV are CP1 and CP2 - they allow the ABV to open when all the 2-Way Valves are closed because the pressure from the pump, that is normally directed to the HW or CH, is now forced down the ABV pipe. The others either don't or are not reliable and the Grundfos tech manuals also advise against. Most definitely must not use PP1 or PP2 Proportionals as the pump slows down when the 2-way valves are closed and that means the ABV won't open.

    Works very well here. It was all easy to check just by holding the pipes and switching everything in different permutations and feeling the temperature differences in all the pipes as the different valves opened and closed.

  6. #26
    Automated Home Sr Member electronicsuk's Avatar
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    Quote Originally Posted by emmeesse68 View Post
    What I observe is different. Valves and boiler are driven independently, so sometimes the boiler is fired when all valves are actually shut. An open radiator or a spring-loaded bypass could take care of this but, computer-wise speaking... if you can fix it in software, what's the point of changing the hardware?
    Sounds good in principle, but I'm not sure it would work for everybody. For example, it's could have a nasty impact on temperature overshoot, especially for anyone with oversized radiators and/or a large system with a lot of water volume in the pipework. I'm not even sure it could be done without changes to the evo hardware - it doesn't seem to me that the communication between valves and the controller is regular enough.

  7. #27
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    Quote Originally Posted by electronicsuk View Post
    Sounds good in principle, but I'm not sure it would work for everybody. For example, it's could have a nasty impact on temperature overshoot, especially for anyone with oversized radiators and/or a large system with a lot of water volume in the pipework. I'm not even sure it could be done without changes to the evo hardware - it doesn't seem to me that the communication between valves and the controller is regular enough.
    Don't think letting the boiler overrun circulate through a radiator (when the flame is off) would cause temperature overshooting. Especially when large radiators are involved, hot water would already be in the radiators when the flame stops, regardless the valves being open or closed... thus overshooting in any case. I think the Evohome Learning technology is supposed to take care of this, after it learns the heating cuve...

  8. #28
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    Firing the boiler when valves are shut is never good practice. It has nothing to do with preventing overshoot either. If an overshoot is about to happen, just don't fire the boiler anymore.

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