Vaillant Ecotec Plus 832 Delay in modulating up

2 Nov 2016
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United Kingdom
Hello all,

I have moved into my new house which has a Vaillant Ecotec Plus 832. DHW is fine but I just need to confirm the CH is behaving correctly as I couldn't see any other posts with this issue.

The Honeywell CM907 wired room stat calls for heat,
Boiler fires up, burner at full 2 seconds then reduces right down to near minimum,
Target temp climbs very slowly until 5 mins has passed,
Then burner modulates up and target temp of 60 degrees is achieved within a few minutes, and modulates down and keeps stable target temp of 60.

Once the room stat has reached my target of 22, it will then cycle the boiler to keep the temp stable.

But when it calls for heat, the CH temp is only 45 degrees with the burner low, and the burner doesn't increase until the 5 minute delay, then it would modulate up and reach target temp BUT before that happens, the room stat clicks off again.
Repeat cycle but target temp is never achieved again unless the room stat is calling for heat longer than 5 mins (if I increase temp above PB of room stat)

I have checked through other posts and have put some relevant info below to help.
In the menus
Partial load is set to 15kw
Pump over run 5 mins
Pump speed auto
Anti cycle 20mins
System on 8mm microbore
All rads do get hot at the same time after the 5 minutes have elapsed.
Once the system has been running, target 60 and return 54

Is this normal behaviour because the room stat is clicking alot and the rads are barley luke warm, ocassionly the room stat will drop below the target by 0.5 degrees because the flow target temp doesn't get much of a chance to get there within a 5 min burn.

Room stat increase minimum on time to 5 mins max.

5 is the magic number (y)

Thanks in advance
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You're probably better setting the cycle rate on the CM907 to 3 (the oil boiler setting). Thats the trouble with Honeywell's TPI control, its an on/off signal to the boiler, you will get a lot of switching on/off when close to the set room temperature, thats how it works.

But as well as the lower cycle rate, it may help raising the flow temperature on the boiler to 70C, setting D.14 to 5, and extending the pump-overrun to 8 minutes with a lot of 8mm microbore in circuit.

IMO Vaillant's controls are better at maintaining a even room temperature as they automatically reduce the flow temperature as the room temperature is achieved . However, you only have one choice of 'on' room temperature with a VRC470 or a VRT350 against many with a CM907
Ok thanks the831Bunny.

Is the 5 minute delay before burner modulation increases a software 'feature'.

Do other users of ecotec plus models notice a similar delay when partial load has been set instead of being at 'auto'?

I will try changing the setting you suggest and I am leaning towards purchasing a Vaillant room stat as previously mentioned
Apart from the initial burn, subsequent requests for the boiler to light through 'on/off' controls are made when the property has reached its temperature and the room thermostat is requesting heat again. These subsequent firing requests require a lot less heat input once the property is warm. So to help with overshoot and boiler efficiency the low start is a feature of every firing cycle. It's a step towards helping on/off controls maintain an even room temperature. This is very much less of an issue with Vaillant's controls, as the flow temperature reduction produces extremely long burn times which while keeping the room temperature even reduces the return temperature raising the efficiency.
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Its the OP who should not be opening the front cover of the boiler!

More likely to be sent to the gallows than the Tower, that is over £20 now!
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Ok thanks Bunnyman & The831Bunny for the settings info, will give them a try.

Whilst appreciate what the boiler is trying to do, coupled with an room stat on/off control. I can't understand why there is alway this 5 minute delay, even if the heating circuit hasn't been used for a couple of days and the circuit is 'cold', when I switch it on, I would have thought it would ramp up the burner when seeing such cold flow / return, not wait 5 minutes

Can anybody who has an ecotec plus confirm this happens with their boiler, no matter what the conditions, after firing the boiler waits 5 minutes before increasing the burner?

Just hoping this isn't a fault, but will call out my friendly local engineer if I need to :)
Myself and @Bunnyman work on these boilers all day everyday, rest assured it's a normal function. The interruption by the TPI function of the CM907 is bringing it to your attention.
To be fair, if your property has achieved its set point temperature (by the 907 turning off and doing its job), then job done. If it has achieved it with the boiler still on low input, then it has achieved it in an efficient way. The boiler only knows On or Off with 240v controls. Don't be hung up on the boiler having to reach its set flow temperature, you only need this when the outside temperature is below 0C. As long as you are warm and the property temperature is stable around your 907 set point, then as I said, job done.
Ok thanks.

Think I have been reading too many posts on here and getting obsessed with flow / return temps. Whatever happens, it's got to be more efficient than the circa 1994 boiler I left behind!

Your are correct, as long as I am warm and temp is stable, job done.

I think having the loud CLICK of the CM907 about six feet from where I sit in the lounge brought it to my attention.

I will try the settings you kindly advised, over the next few days and see if thats got it.

Also I am considering changing the CM907 programmable room stat to one that can be remotely operated over the internet via an iOS app as my work pattern can sometimes mean I don't come home until late and don't want it warming the house up from my set time of 4.30pm

I would prefer
1- Something apple homekit compatible but not the end of the world.
2- That doesn't contain a loud relay in the room stat but possibly wireless so the control relay is at the boiler.
3- Is 7 programmable with various times / temp per day.

Could you Bunnies who work on these advise what you install and find works best, maybe something not so on/off but with the ability to remotely turn down / delay the heating of the house if needed

I had considered Ecobee 3 but that is not available for UK wiring yet, only US with 24v AC relay needed, but then again, I am back to the on/off problem.

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