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  1. robj20

    robj20 Member

    So 3 times now i have had this issue with my boiler turning the burner off because it senses an error on the flow/return temp sensor.
    Had ideal round to check it out, no faults found they changed the sensor anyway and left me a spare then monitored the system for a while and noted that occasionally the boiler would read the return temp higher than the flow and that with the system set to off the boiler then fired up again a few minutes later (he was unfamiliar with Evohome, and i know when you set the heating to off it can take a number of minutes to actually fully switch all zones off). He did suggest opening the auto-bypass more but otherwise said the boiler is working fine.

    On thinking about when it seems to do this, i'm wondering if its when Evohome has so little demand for example one radiator on the lowest setting, the auto-bypass is flowing the majority of the water and as this circuit is so short and no where for any heat to go this causes the issue.
    But could it also be not open enough and when the water suddenly has no where to go it senses a spike in return temp.
    Anyway to figure out exactly whats causing this or should i just open the valve another 2 settings?

    This is the specific fault. Pressing Restart gets things working again.


    Any advice would be appreciated.

    I do actually have a photo of the valve and you can see its set between 0.2 and 0.3.

    Last edited: Jan 4, 2018
  2. Vee

    Vee Plumber GSR

    Yes, you are going in the right directions. These sorts of systems are usually associated with insufficient bypass during low demand. Depending on which boiler you have there is a chart which gives details of the minimum flow requirements through the boiler. A correctly sized pump, system resistance, length of pipe run to bypass and setting of bypass all play a role in this and need to be set up to suit your particular system. This rarely happens on installation or replacement of a boiler as it can be time consuming. The installation of Evohome controls does test the adequacy of the setup to its limits. Best to start with just adjusting the setup and ensuring the system is balanced well.
  3. Vee

    Vee Plumber GSR

    Symptoms instead of system in the second sentence.
  4. robj20

    robj20 Member

    I cant seem to find a graph for my boiler Ideal Vogue Gen2 Combi C32.
    There are two settings for the pump as well in the boiler menus i'm unsure which i should have it set to if it even makes a difference.
    Comes under Pump Modulation 70% (equivalent to 6m head) and 100% (7m head)
    The boiler does have the option to plot graphs its self if any of these are useful in figuring out the settings to use.
    Water Pressure, Switch Live, DHW Flow Rate, DHW Temperature, Flow/Return Temperature, Flame Status, Outside Temperature or DHW Switched Live.
  5. Vee

    Vee Plumber GSR

    You need to read between the lines in your installation and servicing instructions Section 1.13 and 1.18. As the heating output for this boiler model does not appear to be range rated, it may well need to compensate via the bypass for excess output on the CH side. The CH output is 4.6 - 26kw for your model. The upper is rarely required for the scenarios these boilers are put in and therefore there is an issue of oversizing of the boiler regards the heating as the DHW takes the lead on sizing. Often these boilers fire on high gas rate to start which then can cause the machine to think there is insufficient circulation when it encounters minimum demand. Admittedly I cannot find any data regarding minimum flow so the 10% is the closest we are going to find. Set the bypass to fully open and give it a go. After that you will need to increase the capacity of the bypass until the boiler is happy. Make sure the next boiler is capable of being adjusted to suit the output. Best to spend a little extra to get those features.
    • Like Like x 1
  6. robj20

    robj20 Member

    I did see that 10% of the heating demand.
    What I might end up doing is having my yet to be fitted bathroom radiator on dual lock shields. Put a thermostat in there so it can call for heat. The only downside is that the bathroom could end up over heated, but that's less of an issue for a bathroom anyway.

    I could also move the bypass as far away from the boiler as I can so it can lose more heat. This would be on the landing so another 5 or so meters of 22mm pipework.

    Ideal have said I should try the bypass set to 0.4 if it is currently set to 0.3.
    Does that increase the flow through the bypass or decrease.
    Last edited: Jan 4, 2018
  7. gmartine

    gmartine GSR

    Fit your bath rad without a TRV before doing anything and don't excessively trim your TRV's with your new toy , your boiler will be happier with a bit more load rather than trying to run every rad at the minimum possible temp.
  8. robj20

    robj20 Member

    What do you mean by trim trvs.
    I think the bypass radiator is the easiest option until boiler makers make the boilers work properly with fully zoned systems.
  9. Vee

    Vee Plumber GSR

    I would go for the bathroom rad on lockshields. No thermostat otherwise it will shut it off. The bypass will only open if there is low demand so changing the setting should not affect normal operation.
    The TRV's (or Evohome heads) will trim with set temperature to suit the demand and timing set. The extending the bypass loop is also an option.
  10. Vee

    Vee Plumber GSR

    There are many manufacturers who make decent boilers that are capable of operation with these control systems. I do not consider Ideal to be one of them. They are a budget brand.
  11. robj20

    robj20 Member

    Too late for that now though.

    Any input regards Ideal response.
    "Ideal have said I should try the bypass set to 0.4 if it is currently set to 0.3.
    Does that increase the flow through the bypass or decrease."

    I suppose when it was fitted they just set it to the middle, maybe its flowing too much.

    Also what do the pump settings change i have a 70%(6m head) and 100%(7m head) modulation option.
  12. robj20

    robj20 Member

    I have had an idea. Not sure if its possible though.

    Can i remove the TRV valve from the hall radiator, fit a lockshield in its place.
    Then i could run that pipe to the cupboard under the stairs (about 1 meter away) where i can have a HR92 on a the TRV valve to control the radiator remotely, you could do it under the floor but it needs batteries changing every so often.
    I then also between the TRV valve and lockshield under the floor T in the bypass return, so that it now bypasses through the radiator.

    Would that work or is there a reason ABV are 22mm and i cant get the required flow through a single radiator?
  13. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Or put the rad just on lockshield valves (so it's always there) and pipe the rad up before any zone valves

    That will work for sure
    • Like Like x 1
  14. gmartine

    gmartine GSR

    70% modulation should be enough and turning the bypass from 0.3 to 0.4 bar effectively makes it more difficult to open, the return temp is the issue so you could also try reducing the boiler flow temp.
    • Like Like x 1
  15. robj20

    robj20 Member

    I don't have zone valves each radiator is a zone. That would work yes but also means the hall then couldn't call for heat independently.

    Evohome controls the flow temperature automatically. The dial on the boiler is disabled.
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