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Thread: Vaillant 831 Ecotec Plus going over set temp

  1. #1
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    Default Vaillant 831 Ecotec Plus going over set temp

    Noticed a strange thing with my boiler over the last couple of days,the set temp is 65 degrees but when I've checked d40 it's going between 5-8 degrees over the set temp.My boiler is the Vaillant 831 Ecotec Plus running Honeywell Evohone with opentherm,the boiler has the Vaillant Vr33 fitted to enable opentherm to work.My boiler is about 12 years old now and I have read somewhere that a number of these came out of the factory with the ntc sensor on the flow pipe inside the boiler fitted in the wrong place on the pipe,don't know if anyone else has had a similar issue. obviously what is happening is that because it's going over the set temp the boiler is shutting down because it starts to bring the return temp up,all my rads heat up evenly,seven rads all fitted with Hr92 valves including a smiths plinth heater in the kitchen,this has a separate Honeywell Rf87 wireless stat doing the temp sensing,boiler has an internal bypass.I have also range rated the boiler as it's too big and wasn't sized correctly by the installer.The output is 8.9Kw-24Kw on the heating output.
    Last edited by garymtitley; 18th January 2022 at 01:22 PM. Reason: Spelling mistake

  2. #2
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    Do you have the ability to measure the actual Flow and Return temperature of the boiler, rather than relying on the boiler's read out?

  3. #3
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    Hi Bruce,no I haven’t unfortunately.D5 on the boiler reads 70 which is what I have it set at,D40 is where I can see it’s going over it’s set temp and eventually the return rises up to meet the flow temp as a result.When the boiler is running without going into any settings I can watch the temperature on the display and again it is going over what I set the boiler at,this happens whatever temperature I try and set so it’s ignoring the set temp and it’s sometimes as much as 8 degrees over,not sure why it’s doing this.
    Last edited by garymtitley; 20th January 2022 at 08:43 PM.

  4. #4
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    For the moment as a work around why not just set the Max flow needed as 5C lower than what you actually want. See if that helps.

  5. #5
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    Thanks Bruce,yes that's what I've done as a work around but it still goes over by the same amount but at least it doesn't go sky high and bring the return way above where it needs to be.

  6. #6
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    You need a heating engineer to look at your boiler

  7. #7
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    Going to get one booked and see what’s going on and the boilers about due it’s annual service/check.Found someone not far from me that knows a lot about Vaillant boilers so I’ll keep the thread updated once I get it sorted.

  8. #8
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    I think you might benefit from getting a temperature sensor. Useful for balancing radiators too. What we don't know is if the boiler's NTC is duff or not.

  9. #9
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    Yes I think I will get a temperature sensor,would an infrared one be ok?Phoned the vaillant repair company near me yesterday regarding my problem and after giving him lots of info and telling him that my system is running Evohome and opentherm and obviously the problem,he said what did I want him to do,my reply was I wanted it looked at and fixed,his reply was to suggest I turn down the flow Temperature,I quickly realised that it was a waste of time and he wasn’t interested so the call ended,about as much use as a chocolate fire guard springs to mind.I do use someone to check and service my boiler but I don’t know how much in-depth knowledge he has when it comes to things like NTC sensors.May order two new NTC’s for the boiler and get him to change them as a matter of course,they cost much.

  10. #10
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    Quote Originally Posted by garymtitley View Post
    Noticed a strange thing with my boiler over the last couple of days,the set temp is 65 degrees but when I've checked d40 it's going between 5-8 degrees over the set temp.My boiler is the Vaillant 831 Ecotec Plus running Honeywell Evohone with opentherm,the boiler has the Vaillant Vr33 fitted to enable opentherm to work.My boiler is about 12 years old now and I have read somewhere that a number of these came out of the factory with the ntc sensor on the flow pipe inside the boiler fitted in the wrong place on the pipe,don't know if anyone else has had a similar issue. obviously what is happening is that because it's going over the set temp the boiler is shutting down because it starts to bring the return temp up,all my rads heat up evenly,seven rads all fitted with Hr92 valves including a smiths plinth heater in the kitchen,this has a separate Honeywell Rf87 wireless stat doing the temp sensing,boiler has an internal bypass.I have also range rated the boiler as it's too big and wasn't sized correctly by the installer.The output is 8.9Kw-24Kw on the heating output.
    Maybe the boiler is just bordering on shutdown if its minimum output is = or > the heating demand, boiler shutdown occurs on most gas boilers at flow temp SP+5C (to 8C). Obviously if the heating demand is > than the boiler minimum output then not the reason.

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