Vaillant "D" Settings help

[pd1971]

Hi

Just had a new Vaillant 418 installed to replace a Ideal minimiser ff30 which has a 10KW output

Was going to go for the 415 but was advised to go for the 418 by 2 different companies - so took the advise

My monthly gas bill used to be about £35-50 per month with the old boiler
Have monitored a few days usage & it will result in a bill of about £80.00 approx

After reading quite a few forum posts - understood that the boiler can be rated down with D0 setting

After checking the total heating requirement the boiler - I really should have gone for the 415 which would have been more than enough -oh well lesson learned

Hall way rad is switched off so this equates to about 6 KW + 2KW for the HW

The boiler wasn't changed from the default settings by the installer

The rad water temp was set by the installer to 73°C this was very uncomfortable heat
So I dropped it to 58°C which was much better

Property is a 2 bed end terrace built in 1997

Back bedroom 3364 btu/h
top of stairs 1047 btu/h
bathroom 1365 btu/h
front bedroom 2883 btu/h
lounge rad 1 4852 btu/h
lounge rad 2 2426 btu/h
hallway 1365 btu/h
Kitchen 2426 btu/h
toilet 1047 btu/h
20775 total

I'm now trying to get the boiler to the most efficient settings
Last night I set D0 to 10 would you recommend going any lower

The boiler is now firing for longer which I believe is better?

Are there any other setting I need to change

Thanks in advance

Dave

 

[Agile]

Every time I hear about these high gas bills they result from incorrect assessment and comparisom.

Your Minimiser was about the same efficiency so dont expect any increase!

I am so sorry you had unskilled installers advising you.

A modern house like yours is unlikely to need more than about 5-6 kW for heating!

Hot water heat up should be timed to be 30 min BEFORE the heating is due to start.

Set d0 to 8 kW and that should be fine. You will then have an 18 kW boielr runnign at less that half power as a monument to the monumental stupidity of your installer!

Tony

 

[pd1971]

Hi Tony

Thanks for your reply, really appreciate your advise

That's what I thought ..... wish I'd taken advise from yourself prior to the install...I'm sick & tired of getting bad advise & workmanship from workmen & installers

Hall way stat is set to 21

Just checked the flow & return temps after the boiler finshed firing for 6 minutes

Started at
D40 - 37
D41 - 23

end of firing
D40 - 47
D41 - 34

Does that sound about right

What would you suggest for the rad water temp it's currenty at 58°C bearing in mind I've lowered the boiler output

Will try setting for D0 down to 8

regards

Dave

 

[Agile]

Those sound fine.

But the 47° is a lot lower than your set 58° ???

But what does the boiler display show when it goes off?

Do you know why?

If you can get enough heat with such a low flow temp then it will be will condensing and very efficient.

Tony

 

[pd1971]

Great Thanks Tony

That's what I thought, not sure why they were so low?

The rad water temp is set to 58°C so I expected the flow to have reached that temp

at the end of the last firing it was
D40 - 47
D41 - 34

It's just fired again after 30 minutes & just stopped at

D40 - 56
D41 - 43

Dave

 

[gaswizzard]

I am so sorry you had unskilled installers advising you.

A modern house like yours is unlikely to need more than about 5-6 kW for heating!

Heard it all now

Hot water heat up should be timed to be 30 min BEFORE the heating is due to start , set d0 to 8 kW and that should be fine.

8kw to heat a standard tank in 30 minutes?

Crank her up as turndown ratio should take care of it. , too low an output rating WILL cost more to run , false economy.

 

[pd1971]

Hi gaswizzard

What output would you recommend - it's not an issue of the HW taking longer to heat - if more economic?

The old boiler output was only around 10KW & that was fine

Dave

 

[gaswizzard]

Doubt if 6 kw would get the house up to design temps when the outside temp hits minus X , the burner wouldn't shut down.

If it's the 2nd gen vaillant then auto should take care of it.

 

[pd1971]

As far as I'm aware its the latest one label behind the door states

VU GB
186/2-O H

Are you suggesting I should leave it at 18KW?

 

[gaswizzard]

Good luck , can see you getting an earole from the Mrs.

 

[pd1971]

Well have been running the boiler for the last 2 days, it was using about 60KW / day when set to 18KW & the rooms weren't staying hot that well

Did try on D0 to 8KW but the boiler was constantly on

Have set to D0 to 9KW & it's much better temp in all the rooms plus I'm now using about 37KW which is about what I used to use with the old boiler

So thanks to Tony for your advise

I do find that the boiler is firing sometimes for about 10-20 secs then going off & the temp display shoots up rapidly is this normal?

 

[Agile]

I do find that the boiler is firing sometimes for about 10-20 secs then going off & the temp display shoots up rapidly is this normal?

This will happen when all he TRVs are satisfied !

GW was trying to comment that at 8 kW the cylinder would not be fully heated in 30 minutes!

But I only said that the HW should be times to START about 30 min BEFORE the CH starts, then the HW CONTINUES to be heated if needed during the CH.

He does not realise just how little heat a modern terrace actually needs. Boilers only have a modulating ratio of about 3:1 so your minimum output power will be about 6 kW at which the boiler will be into on/off modulation.

Of your 37 kWh lets assume that 5 kWh is for water heating then how many hours is the heating timed for? That will give the actual heat loss of the house!

Tony

 

[gaswizzard]

Hi

Just had a new Vaillant 418 installed to replace a Ideal minimiser ff30 which has a 10KW output


My monthly gas bill used to be about £35-50 per month with the old boiler
Have monitored a few days usage & it will result in a bill of about £80.00 approx

Bearing in mind the quarterly tariff set for gas usage is around 8.5 pence per kw upto 650 kw with usage over 650 kw reduced to 3.55 pence then.................

£35.50 month/30 days = £1.16 per day.

£1.16 / 0.085 pence = 13.6 kw per day.

So the existing boiler was on for a max period of just over an hour each day? , what is the size of HW tank? something doesn't quite add up with your figures , if you are using a prepayment meter then gas usage is charged at around 6 pence per KW which would equate to around 19 kw per day.

£80 per month would equate to around 31kw per day , some would give their right arm if gas usage could be this low.

 

[Agile]

Most of these DIYers attempts to compare gas consumption become seriously flawed because of the outside temperature variations.

You can only compare exactly like for like! The heating hours may be the same but the outside temperature fluctuates widely.

Under normal settings the range of temps are from 21 C downwards so 1 C outside would use twice as much gas as 11 C.

Even these examples are not exactly linear because colder temps often coincide with higher wind speeds and house cooling goes up when its windy, particularly artic gales of -1 C from the NE.

Tony

 

[scoobydo123]

What is the hot water cylinder tank stat set to? If vented cylinder shouldn't we be looking for water stored at 55 as a minimum. If boiler stat is only at 58 are you struggling to get that satisfied?

Also you mention that sometimes it only fires for 10 to 20 seconds, this sounds like the famous Vaillant gas rate too high for subsequent burns if stat is not satisfied after initial burn (see paragraph one). Would be very interested in a test for this by having cylinder stat satisfied, cranking it up till boiler comes on (ensure that CH cannot call during this test). The boiler will hopefully fire for a nice long first burn and modulate down towards the end (assuming not too much latent heat in primaries) eventually the boiler will cycle when delta is too close. Now watch the boiler to see what it does when it fires again, is this when it only burns for 10 to 15 seconds?

What is your anti cycle timer set to?