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I

icezebra

So, recently had the Vaillant 350f thermostat replaced with a Nest and I'm left with a problem I can't wrap my head around. Boiler is Vaillant ecoTec 831 Plus and is only a couple of years old.

With the Vaillant thermostat, the flow temperature would vary based on room temp vs set temp, but also quite regularly reach the max flow temp of 75C. Now with the Nest, which as far as I can tell is now contact closure only, the flow temperature never goes above 55C.

I can't see anything in the Nest settings about controlling flow temp, and if it's a straight switch then I can't imagine how the Nest's settings would impact it. The only thing I can think is that there's a boiler setting buried in a menu to do with this.

Tearing clumps of hair out. The house is noticeably colder as some radiators now just don't heat up as much. And rather than 30 mins to take the room with the Nest in from 19C to 21C, it now take hours; and doesn't even get there. Haven't even managed to get the room above 20C.

Help! Anyone have any thoughts? I'm not 'Registered Professional Gas Engineer' so am not going to play with the innards of the boiler, but following a chat with a Vaillant installer - who had no idea, I'm trying to get an idea what this might be (and hopefully buried in settings) before I pay for someone to come round.

(Have been searching for previous questions ref this issue to no avail.)
 

ShaunCorbs

Staff member
S. Mod
Plumber
Gas Engineer
does nest do weather comp?
 
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I

icezebra

It does, based upon location and internet based weather. But at times it's been bloody freezing outside, and still flow temp doesn't get about 55C. Besides, can the Nest request different flow temperature over simple on/off contact closure link? The weather comp I thought was mainly about time in advance start heating to reach target thermostat temp.
 
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N

newcastle phill

The nest device is a fancy thermostat. It has no control over the flow temp. Just the room temp afaik.

It has no means of talking to the boiler to read the flow temp. They can learn a few things re time -to-heat etc but not that.
 
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N

newcastle phill

Having said that its been a while since I fitted one and at the time opentherm wasnt properly implemented. If your boiler is opentherm and you have the new v3 nest it may be able too. You need to check your boiler compatability
 
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I

icezebra

Thanks. Nest v3 supports OT, but can't find any mention in the UK Vaillant manuals ref OT. Some searching online suggest Vaillant NL is a member of OpenTherm, but Dutch manuals aren't helpful and models seem to be different. Some suggestion online about Vaillant UK not really supporting OT and anecdotal sources about warranties / possible firmware upgrades etc.

Even then, strikes me as unnecessarily complicated though - the boiler, if undergoing c/c activation, should just try to reach target flow should it not - without any kludges with OpenTherm?
 
OP
N

newcastle phill

Yes sadly so far when something is opentherm it offers no guarantee of compatability. Its down to manufacturer implementation.

Opentherm is a set of instructions and
Methods of control.
Some manufacturers may only support parts of it.

Some boilers released early on at the dawn of opentherm time only supported very little and required add on looms to be added to offer more functionality.

Have you called Vaillant.
They use a proprietary system called Vsmart. They should tell you if they fully support opentherm
 
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Chalked

Esteemed
Plumber
Gas Engineer
Vaillants do not have open therm and nest can only alter the room temp. It has no control over the boiler.
Have you removed the complete recoiever from the front fascia? Look in the boiler settings and see what temperature it's set on.
 
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I

icezebra

Boiler temp settings are at 75C max. Key thing you said there - I believe the receiver is still there! This sounds like the problem. Boiler is expecting to be told flow temp, but only getting on/off. Brilliant. Off to check this (and get 'Registered Professional Gas Engineer' person to remove of course) and will update. But I think you've resolved it!
 
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I

icezebra

Resolved! Receiver was still plugged in to front of boiler and as I didn't need to remove the case, I've just popped it out. Flow temperature rising higher already. Thanks Chalked!
 

Harvest Fields

Esteemed
Plumber
Gas Engineer
Advent Win
My understanding of nest is that it monitors local outside temp and your heating patterns and combines the 2. So as a smart stat it may decide that during the warmer days it is not necessary for the boiler to be working so hard. (But I have been wrong before):p:p:p:p
 
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