Vaillant EcoTec 831 - Help with setup

[Ian Clarke]

Apologies at start for long post but trying to give as much info as possible,

Home - detached bungalow build 1989, cavity wall insulation, loft had extra in 2008, doubled glazed, 2 bedroom, 1 bathroom.
Size is Width 35 feet, length 32 feet, room height 8ft.

7 Radiators as follows installed 1995 plus 1 towel rail.

Boiler replaced in 2011 when had magnaclean added and hotflush and sentinel x100 in system.


Room Stat - Vaillant VRT350F - in analogue mode, in lounge 5ft up wall - receiver in front of boiler RF signal 9. Set to 20c

settings on boiler

D0 - I believe with above if my calcualations right - 12, 15(read pump flicks to 2nd speed at 14.4) and the default 24. please advise best setting
D1 - set to 8
D2 - 20 (default)
d71 - 75 (default)

the d40 and d41 varies as the VRT stat does seem to modulate it.. can be as low as 40 or as high as 75.

at the moment d40 - 75, d41 - 59

I am using approx 75Kwh a day by end of the day. Even when stat reads 20 and stays at that all the hour, the boiler is kicking in and out and uses approx 3.5Kwh during that hour


Any help/advice be much appreciated.. Thanks in advance

 

[Ian Clarke]

I have noticed it seems to constantly want heat, s4 even when temp is reached. Any help appreciated

 

[ScottishGasMan]

Sounds like its all working fine. If you set room at 20 degrees your going to use gas to maintain that 20 degrees, so using 3.5kwh sounds fine. The colder it is outside the more gas it will burn to maintain that 20 degrees.

D0 - set to whatever you think your heatloss is. The rest of them leave as they are. May be worth turning the CH flow temp to 55/60 degrees and see if thats still high enough to heat the house ok, lower you can keep the flow temp the more it will condense

 

[Ian Clarke]

Can you tell me does the 350 take the max from the control knob or the d71 setting, as Vaillant tech struggled to answer that. if I turn the knob 60 without changing d71 would the modulating go all way to 75 or stop at 60 - thank you so much for your time ?

 

[rbranco]

d71 limits the max the control nob can be set to so the VRT should not go above that, if you lower the temp down to 65 then the boiler should run a longer burn between turning on/off, it may not even turn off, but running it lower you should look for d41 values around 50c or below to keep the boiler running as efficient as it can.
If you find that the d40 temp is going too high then boiler turning off, then you could try turning d0 down a little, but do your house calculations.

 

[Ian Clarke]

Thank you all for your responses, definitely helping, observations this morning, is house nearly at temp in an hour, good, and not used as much gas, also good, but noticed boiler runs S4, but goes past preset 60 ch and then goes into s7 and rad flashing (anti cycling) but not s8.. is this because d0 set to low or high or just normal operation for this boiler as seems to do it more closer to the temp required, stat wants 20 room on 19 ?

D0 set to 12.

I read take number of rads and times by 1.5 to get figure. So 7 rads plus towel rail 8 x 1.5 = 12 was the logic or how do I size it ?

Home Size is Width 35 feet, length 32 feet, room height 8ft. - Detached Bungalow

Rads

Lounge (where room stat is) - Double 1100 x 600 (double fins) - No trv
Hall - Double 1200 x 600 (single fin) - TRV 3
Bed 1 - Single 800 x 600 (single fin) - TRV 3
Bed 2 - Single 1400 x 600 (single fin) - TRV 3
Dining - Single 1100 x 600 (single fin) - TRV 3
Conservatory - Double 800 x 450 (double fin) - TRV 2
Kitchen - Single Stelrad Compact K1 - 1000 x 700 - No Trv
Bathroom - Towel Rail 500 x 800


Thank you all for your help again its much appreciated.

Settings at moment

D0 - 12
D1 - 8
D2 - 20
D71 - 60

 

[rbranco]

You need to get the BTU/KW value for each radiator, then calculate total requirement. Download steel rad catalogue to get guide figures. Then knowing heat loss of house to then finalise the calculation.
If you have lowered it so much nad it keeps tripping out then you may have a flow rate issue, pump, blockages etc.
I've had to replace my pump after 12 years as it started to get very slow and got blocked with magnitie flakes which made it overshoot temp and I had to reduce d00 to 10 at its worst, now new pump and flushed system, all great now. I have open vent system though.

I've got 3 bed, 2 living room, 1910 house, kitchen extension, bathroom. Rooms are large 4m Square and up to 3m high etc and my rads only need 12kw but as house is solid brick its very lossy so boiler runs at 16kw just fine with 65c flow rate. I've got lots of single rads. So your requirement seems less than mine.

 

[Ian Clarke]

hi thanks for the advice, so downloaded catalogue and got the watts figure per radiator and found towel rail online and comes to 9,495 so 9.5 kwh or 32206 btu which coverts to 9.43 kwh which I'm guessing is if all running flat out per hour.

They won't be as TRV valves not on Max settings, so do we think d0 = 10 be better or am I simplifying it too much ?

 

[rbranco]

Give it a try, see how your system runs, if it overshoots and if it maintains adequate temperature.
What boiler do you have 4xx/6xx/8xx etc, do you have any other VR modules installed?
Do you have a HW cylinder, what etc?

 

[Ian Clarke]

It's the ecotec plus 831 combi so no HW cylinder.

hot water is fine too, house is warm and only the VRT350f no other VR modules for weather comp etc.

VRT350 modulating and just checked d40 was 49, d41 was 40 which I know not the 15 difference but I suspect that difference is when running flat out, have seen flow/return difference of 17, but normally around 9/12 difference.

 

[Ian Clarke]

looking at the Stelrad catalogue the elite series I got designed to run at 75/65 so setting d71 at 60 might be too low. I think d0 - 10 but d71 - 65 probably better even though the 350 modulates that down anyway.

 

[rbranco]

Doh I was looking in the first post but you had written it in the post title, slow morning for me.

Do not get too hungup on the d40/d41, as long as the house satisfies in acceptable time, boiler does not keep overshooting and the return temp is at/under 50 then its working well.
Give it a few days as today may not be as cold as tomorrow etc and as you have no Weather Comp you may find the need to adjust d00 slightly in winter to summer.

Now as you d00 is lower it will raise temp slowly but eventually as house heats up you will get to an equilibrium where the boiler is firing just enough (its modulated down) that the flow stays at the max CH you set and return flow is 45-50, normally it will start at max power (d00 limited) until flow reaches temp, problem is there is a time lag between when D40 says its at temp and the boiler starting to scale back which is why it can overshoot when D00 is too high.

I would set D71 to 70 and just put the dial to 65, I have my flow at 65 and return comes back at 45-50.
Its a balancing act between heat loss of the house and heat transfer of the radiators. But also without WC you may be setting it up for today but later could be a cold front and house may drop temp for a while until it comes back up to temp. Consider in the longer term to upgrade to WC, it should save you some money.

 

[ScottishGasMan]

Take into account that a 10kw heat loss on a boiler with a heat exchanger and pump designed for 30kw is rarely going to manage a 20 degree flow and return difference.

If you strangle the radiators to get 20 degrees then your also dropping the heat output of the radiators so in effect reducing their ability to get heat out.

The most practice solution is to simply drop the flow temperature of the boiler as low as you can while still being able to get the house to temperature, which as said without weather compensation will require a little manual intervention depending on the temperature outside, reducing flow temp in better weather and increasing it in colder weather.

Condensing only starts at around 55⁰ return temp but is most effective much much lower than that.

Mine is set for 55⁰c max flow temp at -4⁰c outside, but in better weather I can have flow temps in the 30s, but this is completely dependant on size of rads and heatloss of each room. Every 5 degree cooler you want to run it at is a jump in rad size, which jumps more and more the lower you get.

 

[rbranco]

Take into account that a 10kw heat loss on a boiler with a heat exchanger and pump designed for 30kw is rarely going to manage a 20 degree flow and return difference.

If you strangle the radiators to get 20 degrees then your also dropping the heat output of the radiators so in effect reducing their ability to get heat out.

The most practice solution is to simply drop the flow temperature of the boiler as low as you can while still being able to get the house to temperature, which as said without weather compensation will require a little manual intervention depending on the temperature outside, reducing flow temp in better weather and increasing it in colder weather.

Condensing only starts at around 55⁰ return temp but is most effective much much lower than that.

Mine is set for 55⁰c max flow temp at -4⁰c outside, but in better weather I can have flow temps in the 30s, but this is completely dependant on size of rads and heatloss of each room. Every 5 degree cooler you want to run it at is a jump in rad size, which jumps more and more the lower you get.

Seems it was sized a combi which always becomes a compromise on the CH imo.
Im fairly sure the pumps in the newer 8xx series are variable speed from what ive seen, essentially a UPS3 but using the PWM input.

 

[ScottishGasMan]

Seems it was sized a combi which always becomes a compromise on the CH imo.
Im fairly sure the pumps in the newer 8xx series are variable speed from what ive seen, essentially a UPS3 but using the PWM input.

Yea, the ERP pumps are PWM so will help to keep a better spread on the differential, but even on the lowest power setting there still putting through a surprising amount of water, spoke to someone else about that not long ago who said some of the grundphos pumps lowest setting was still way to high to achieve wide temp differences at low gas rates.