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Discuss Ideal Vogue "Flow/Return Thermistor Fault" again. in the Central Heating Forum area at

  1. robj20

    robj20 Member

    Boiler, Ideal Vogue Gen2 C32
    Honeywell Evohome with Opentherm.

    Had Ideal out last year and they changed the thermistor, but this year its doing it again.

    Strangely same time of year.

    Suggestions last year from the installer was to remove the Evohome TRV from one radiator to act as a bypass. I already have an auto-bypass as well.
    But i did this so the hall radiator is left partially open, enough that it gets plenty hot but not too loud.

    I find it too much of a coincidence its the same time of year. Its been fine the rest of the time.

    I'm not convinced its purely a thermistor fault, i wonder if its not liking certain temperature readings and shuts down.

    Is it possible the auto-bypass is set wrong and allowing too much past which would increase the return temp close to the flow as the bypass is withing 2 meters of the boiler.
    Last edited: Nov 15, 2018
  2. Chuck

    Chuck Top Contributor!!

    At this time of year very little heating is needed and TRVs are often shut. This can confuse/upset boilers because they can't transfer enough heat to the house. The symptom is normally short-cycling not faulting.

    There are various remedies, typically reducing the flow temperature or opening the TRVs and letting the system be controlled by the main thermostat. None of them are perfect but modern boilers include short-cycling protection and it's only a problem for a few weeks until the weather gets a bit colder.

    This is an annoying consequence of building regulations that require TRVs, boilers that don't have large enough modulation ratios and relatively primitive domestic control systems.
    Last edited: Nov 15, 2018
  3. robj20

    robj20 Member

    I forgot to mention its Evohome, so all but the hall radiator are fully zoned and automatic. Also uses Opentherm so i have no control over flow temperature.

    But i do agree with you that in my mind the issue seems to be more that the return temp is the same or very close to the flow temp. Thus i need to scrub more heat.

    Could the auto-bypass be set wrong and allowing too much hot water past.

    I know nothing about bypasses. Looks like its set in the middle at 2.5.
    Last edited: Nov 15, 2018
  4. Gasmk1

    Gasmk1 GSR

    i would say the bypass is set too low it will easily overcom 0.2/3 of a bar try with it higher set it higher until you find the right setting
  5. robj20

    robj20 Member

    So which way do i turn it, 0.4?

    Its difficult with evohome to set it so the boiler is on but then close the rads down, from what i understand i only need the bypass to kick in when only one radiator is on to reduce the pressure. But now having a bypass radiator it shouldnt even be required.
  6. Gasmk1

    Gasmk1 GSR

    yes try it o.4
  7. doitmyself

    doitmyself Well-Known Member

    The Ideal Vogue Gen2 C32 has a modulating pump. So the auto bypass will open more as the pump pressure increases. The pump can be set to fixed speed in the menu. This should have been done by the installer.
  8. robj20

    robj20 Member

    I have these settings? Currently set to 70%.


    I think i should also try and balance each radiator at the minute they are all open fully except the bypass rad. Going to be interesting trying to keep the boiler going while i balance each rad.
    Last edited: Nov 15, 2018
  9. robj20

    robj20 Member

    This is flow/return at the minute.
    This is when the gas is off but the pump is still going. 35c flow 34c return.
  10. doitmyself

    doitmyself Well-Known Member

    That is what I would expect if the boiler is off. The pump circulates the water which cools down until flow and return temperatures are approximately the same.

    What is more helpful are the temperatures when the boiler is running. There should be a temperature difference of no more than 20C between flow and return.

    The pump has been set to the lower fixed speed.
  11. robj20

    robj20 Member

    This is what it did this morning when the heating requested a +1c to the livingroom and dining room and a +2c to a bedroom.

  12. Matchless.plumb

    Matchless.plumb Trusted Plumber GSR

    Wow what mess with push fits
  13. robj20

    robj20 Member

    What difference does that make.
  14. doitmyself

    doitmyself Well-Known Member

    The 20C differential is spot on. It would be nice to see a graph of the temperatures over a period of time, as in your previous post.

    How is the balancing going?
  15. robj20

    robj20 Member

    Not even started. That's with all valves fully open.
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