Modulation survey, how long does yours take?

[fronty]

I've had my new boiler a month now, this is the first time I've had one that modulates and now I'm just curious how long others people's systems run at full blast before modulating. This is what I saw tonight when the heating came on from cold....

My Viessmann 100 has a little graph with 6 graduations/blocks, for the first 10 minutes it runs flat out 100% at 6/6.

After 10 mins it starts to modulate down, the graph shows 5/6, then after another minute it drops to 4/6, after 15 mins since firing it's dropped to 3/6, then after another 5 mins (20 mins total run time) it's at 2/6. It stays at 2/6 for another 15 mins before finally modulating down to 1/6, so it takes a total of 35 mins since the boiler fired to reach minimum flame height. It then stays at 1/6 continuously with zero cycling until the roomstat registers a 1 degree rise and turns off the boiler, this generally takes about 60-90 mins in total. I could get the room with the stat to warm up quicker (close the door etc.) but then the rest of the house would be freezing!

My system is 26kw with 13 rads. Outside temp is currently 5 degrees, and the roomstat is set to 22. Does any of this sound typical?

 

[Welder]

May I politely suggest you go for a walk with the dog to the pub? I'll wager there are much more interesting things happening there than sitting watching your boiler modulate

 

[JoshW]

I also have a Viessmann 100 (30kw Combi). How it works in practice will depend on the system and how it’s set up. My radiators are only about 8kw in total so my boiler modulates down much more quickly than yours as it doesn’t take long to get the system to temperature. Also it will depend on the CH flow temperature you’ve set and whether you have restricted the maximum heating output in the installer settings.

 

[snowhead]

All a modulating boiler does is match the heat loss of the building.
Every situation is different, even in 2 (apparently) identical houses built side by side.
There are way too many varaibles to compare one boiler to another.

 

[fixitflav]

My Viessmann 100 has a little graph with 6 graduations/blocks, for the first 10 minutes it runs flat out 100% at 6/6.

When the set flow temperature is reached the modulating control adjusts the gas flow down to maintain the temperature (unlike older controls which stop the gas then restart it at a lower temperature). If the rads stay hot while it's modulating there's nothing to worry about.
If the other rooms are struggling to reach temperature before the roomstat stops things you could throttle that rad down, or put a blanket over it. Make sure there's somewhere for the water to go, eg bypass valve, rad without TRV in bathroom etc.

 

[fronty]

May I politely suggest you go for a walk with the dog to the pub? I'll wager there are much more interesting things happening there than sitting watching your boiler modulate

Haha I need to get a dog first!

Thanks for the replies anyway, I was just interested to know how long other people's systems take before modulating all the way down, I dunno if 35 mins is excessive or about right for the number of rads etc. I know there's tons of variables, just interested that's all.

I know, I know, I need to get a life...

 

[JoshW]

If you think it is taking too long to warm up the roads have you checked if the max heating output has been restricted? Mine is set at about 13KW max but it still shows full bars on the graph when it’s firing full on for heat. Yours might be throttled back too much?

 

[fronty]

I have no idea if it's been restricted, I don't think it has because when it's on full chat the meter whizzes round like it's on fire... my old boiler was only 14.6kw and the meter deffo whizzes round quicker than the old boiler, so feels like it's gobbling more gas, and crucially everything gets up to temp a lot quicker than the old boiler. However once it's modulated right down the meter moves real slowly, much slower than the old boiler which just didn't have the capability to modulate.

It's too early to say whether my gas bills will be any different, we had it on pretty much constant over Christmas so already I can see my consumption is about the same as it was this time last year. But with Christmas out of the way it's back onto a timed programme so will see if my gas consumption drops at all. The house deffo feels warmer (and warms up quicker) so that's the main thing, but doesn't stop the wife complaining she's cold...

 

[Riley]

Watching the meter too. Wow you really need a hobby