Vaillant 831 + vrc470f - Hints and tips?

[MisterG81]

So ive just had an aged gravity CH system fully ripped and replaced on a 3 bed semi with a Vaillant ecotec 831 complete with new rads and a vrc470c.

The installer i chose eventually admitted (after installation) zero experience with these "newfangled technology" boiler controls - so has left it to me for the configuration.. this probably means the rads are sized for the rooms rather than specifically for WC.
House is a 3 bed 30's semi with double glazing but no cavity insulation, 8 rads.

Ive read quite a lot on here, and from what i can tell, there are no settings i need to change on the boiler itself, as unlike the 400 series it starts at low flame and ramps up.
The weather sensor is installed on a NW wall.

At the moment ive got the heat curve ramped right up and the target temp set to 30 to try get some heat back into the house as its been unheated for a week.

My plan is to drop the heat curve to 2.0 in the morning and then see how that goes - although at the moment the house doesnt seem very balanced when walking through, so i may need to adjust some TRV/lockshields.

Does anyone have any recommendations?
Im not specifically asking with a problem - more having a log that may help others when searching

 

[Bunnyman]

Curve at 2.3 to start, switch control to modulation, control to stat,

 

[ALEC1]

balancing is important. I live in and end of terrace victorian proprty and have my curve at 1.6... the lower you can run it the more efficient the boiler (but not necesarily less gas used)..

its a great bit of kit, to be fair to the installer, getting training on this control is not easy...

 

[MisterG81]

Curve at 2.3 to start, switch control to modulation, control to stat,

What do you mean by the control?..

Ive got three options that have been covered on this forum many times - "none, thermostat, modulating"

I did try it on modulating at first - and that seems it still fires the boiler on minimum output even when the room temperature is met (43c flow 19c indoors, 8c out) which i assume is going to use more gas in the long run.

Setting the mode to "thermostat" at least shuts the boiler down when temp is met.

 

[Bunnyman]

No it doent use more gas and it keeps a nice constabt temp by modlating rather than overshooting temp or switching on or off all the while this is not only inefficient its not as comfortable

 

[ALEC1]

the trouble with thermostat option is that it only responds to one place, modulating makes the flow temp follow the heating curve...with in margins it appears..

 

[MisterG81]

Ok, ill switch it back to modulating and work with that.

I definitely need to balance the rads though, the upstairs is noticeably hotter than downstairs.

 

[ALEC1]

the point is that if you are getting overshoot the curve is too high....

 

[MisterG81]

the point is that if you are getting overshoot the curve is too high....

Its not an overshoot - the 'stat is in the living room, currently at its requested temp (20c) - the boiler is currently on, maintaining a flow temp of 39c.

Upstairs is showing close to 21c, although usual thermometer inaccuracies apply, but it *feels* warmer when walking into the bedrooms which isnt the ideal outcome.

Ive just worked out that the rads that have been put in have been sized for delta 50... So guess id have to run a relatively higher curve to take it into consideration.

 

[ALEC1]

you are over complicating things, you need to throttle down the top floor rads so more flow goes through the ground floor rads

In effect you are increasing the delta t between the flow and return upstairs to reduce their output, and lowering the delta t downstairs to increase the output..

 

[MisterG81]

I do have another question.. what is a sensible setback temp to use?

previously heating was totally off from 10pm until 5am - for a 6.30 "warm" wakeup.
Ive only owned this house for a few months but the lowest temp ive seen on old heating at 5.30 was 13c.

 

[ALEC1]

6-7c below normal room temp..that way you won't need intense energy to bring it up to target temp..

 

[David937]

Out of interest, how well does your 831 maintain low flow temperatures i.e. without cycling too much? I understand the newer Ecotecs first released in 2012 can modulate much lower.

I have an early 937 which only goes down to 12kw so it really struggles maintaining anything lower than about 50c. It works well on the Thermostat setting though and it does follow the curve I have set (2.3 since we got the house insulated)

 

[MisterG81]

Out of interest, how well does your 831 maintain low flow temperatures i.e. without cycling too much? I understand the newer Ecotecs first released in 2012 can modulate much lower.

I have an early 937 which only goes down to 12kw so it really struggles maintaining anything lower than about 50c. It works well on the Thermostat setting though and it does follow the curve I have set (2.3 since we got the house insulated)

It modulates down quite low - 5kw i believe. it has no problem with the mid-40s flow rate ive seen so far on my 8 rad system, maybe with a bit lower to go.
It always fires up on minimum burn and then upregulates as required.

 

[MisterG81]

Sorry to bump the thread.. but ive got a couple more questions.

1) do i need to bother with changing d.0 down to the 12kw or so that my rads can output?. i dont have any issues with boiler cycling. as this model ignites on min output before modulating up high until approaching requested flow temp when it starts to throttle back.
Im a bit reluctant to change this one as currently with the WC in modulating mode and a curve of 1.9 the house is taking over two hours get to temp with rads that have been sized for delta50

2) Looking at d40/d41 flow and return temps - theres only 4-6c drop between them - on further investigation all the lockshields are fully open. Do i need to start adjusting down the lockshields to try and drop the return temp further?.