Vaillant Eco tec plus 831 issues and high gas usage

[Bushpig]

Hi I am new to this forum so please be easy on me. I am sure i have an issue with my boiler (please correct me if i don't). We moved into new property in Dec (purchased as repo) and previous owner removed the existing boiler from the loft. Anyway i had a brand new Vaillant Eco tec plus 831 with VRT450 Room stat.

My issue is that my gas usage seems extremely high (3 bed detached, loft insulated and i "think" cavity wall.

Now i had problems balancing my system , which i dont think is entirely correct but all radiators do heat up at the same time and upstairs is always 2degree lower than down. This temp is great but my meter is running round at a rate of Knots. I have 11 RADs mostly singles with a couple of doubles and 2x flat tall panel rads in kitchen and room (these two are the worst to balance) . I don't think my return temp is as low as it should be circa 5/7 degree differential . I did get this to 10/11 but lost after re-adjusting rads. The boiler was initially set on AUTO. I have range rated to 15kw, then 13, kw and finally 10kw, but usage is still high. I have lowered the pump to number 1 and have ordered a radiator thermometer to get the current flow. (ABV wound in to stop bypass of flow)

I have taken readings from weds 2pm to 11.30 today:
Weds @ 2pm 8919.33
Today @ 11.30 08936.689

Can someone calculate what this equates to in £amount

Over 2 minutes the last digits in red were : (this was on Auto)
.094
.145

Also when my boiler has heated up and settled should the return temP HOLD OR SLOWLY INCREASE

i AM CURRENT USING approx 6-10 units of gas per day is this right and how mush is this daily. Heating on constant 21 degree 5.30 am to 10.pm and set back to 18 night

 

[bolshy]

Your boiler is rated at 3.34 cubic metres per hour. Approximately 2.4 cubic metres per hour in CH mode from cold would be used, I'd say. When your heating circuit is up to temperature, your boiler will modulate down and use less gas. As your calculation gives 1.53 cubic metres per hour, I would say your boiler is behaving normally. Your heating is on all day. I dont think 16 cubic metres is that much gas over 2 days. Perhaps you should think about improved room temperature controls with heating zones.

 

[Bushpig]

PS

I had a per-payment meter in up until weds 13th , and have received a closing statement showing £30 usage in 5 days.

I have used 20 gas units on my current meter in 2 days

Is this normal , seems very excessive

 

[Tibbot]

On a commissioned boiler, I can't understand what anyone expects an engineer to do with the complaint 'my boiler uses too much gas', any more than if I complained to Curry's that my TV uses too much electricity.

 

[Bushpig]

Thanks Bolshevik that puts me more at ease.

i'm not complaining but looking for advice. The meter is using much less now I have range rated than before . We move from a much smaller mid town house to a 3 bed detached . House before only consumed £40-£50 per month as apAppose to100 to £150. I was concerned there was a problem.

Since winding up the auto diverted valve ( this was dumping too much hot water flow) the boiler is not micro firing or cycling anymore.

I just need to get the balancing right so I can hit a 10-15 differential at the return temps. Can anyone tell me if this is what I Should expect to get and what is the best way to balance . I have so far done this by feel but downstairs rads are harder as to get a decent drop the rads (2 room) become noisy (white noise sound) . I have got a rad thermometer coming so what should I aim for .

Also is 10kw on the boiler enough . House is 3 bed detached with 11 rads most medium size

Thanks

 

[D_Hailsham]

Also is 10kw on the boiler enough . House is 3 bed detached with 11 rads most medium size

Use Whole House Boiler Size Calculator to calculate the heating requirement of your house, then deduct 2kW as you have a combi boiler.

Radiator outputs can be found from the first table in Stelrad Elite Catalogue.

Ideally the rad output should add up to about 20% more than the calculated requirement. This is because the boiler is designed to work with a wider temperature differential (20C instead of 11C).

 

[Bushpig]

Thanks d.Haislham

This comes out at 7.96 with cavity wall insulation
and
12.45 without

How can i tell if this has been done(we have only just moved in). Also i have a garage+Utility (semi converted , no garage door attached (linked detached) that is a usable space and has 2 radiators (kids playroom/utility). if i add this then my output is

12.68
and
15.76

Do these seem right which should i use the 11 rads include the two in the garage conversion

My boiler is set at 10kw seems to heat ok but hot water int as good when it was at 14/15 or even auto

 

[Bunnyman]

Rule of thumb 1.5kw per rad I would set at about 16kw this in d0 is kw output for heating, if ur noticing difference in how water this is ur imagination as that's nothing to do with it

 

[Agile]

A typical three bed semi costs about £1400 a year in gas now, with 90% during the winter months.

You must decide if you want sub tropical temps or economy.

For a start get TRVs for your frads.

Then turn the temps overnight to 10-12-14 C and cuddle more!

You could save 30-40% on your gas bill !

Tony

 

[oldbuffer]

You should have had an Energy Performance Certificate with your purchase of the house. This should show whether the walls have insulated cavities or not. If you have no EPC then it depends on the age of the house.

If pre 1930's then likely to be solid wall, no cavity. May have had additional insulation added externally or internally, but unlikely.

If Post 30's and up to about 60's likely to be cavity, originally without insulation. If subsequently cavity filled look at outside walls for regular marks where drilled holes have been filled.

If 70's to 90's then likely to have been cavity insulated at build.

If post 90's almost certainly cavity insulated from build.

 

[bolshy]

In the North of England there are many houses with cavity walls pre 1930. They started building them in the late 19th century, especially in the North West and Ireland, 'cause it rains a lot with wind driving it. My house is 1926 with full brick width cavities.

 

[ALEC1]

to ascertain if gas usage is high you realy need to work out the £ cost per day..

one of my clients complaint of high energy usage on a dual fuel tarrif..it turned out he as paying £2 a day for a 200m2 terraced house for gas 90 days up to 31 jan... that included some very cold weather...

 

[bolshy]

As for cavity wall insulation, look for siliconed up vent bricks and patched up drill holes. The vents will likely tell you that a cavity wall is present, if there are any injection points, then it's likely that there's cavity wall insulation too. You could go into the loft and look at the top of the wall too with a mirror.
Do you have Thermostatic radiator valves fitted as Tony posted? If so, set them to get 20-21 degrees for downstairs living areas and bathrooms, and 17-18 for bedrooms. What is comfortable is personal preference of course.
And the radiator(s) in the same room as the roomstat shouldn't have a TRV. What's the hot water usage in your home?
Personally, I think trying to heat your home all day on 8 - 10 cubic metres of gas including hot water usage is ok.

 

[Bushpig]

Thank for all your comments , I've looked for cavity wall and can't really see anything , however 2 vents are blocked with steel plate. Others I can't tell if block. The house does retain heat well though and was built in 1977 so possibly has this .

Anyway I have managed to get a return flow of 16 degree differential ( 20 was near on on impossible .

I have set the boiler now at 12 kw as it seemed to be stood at 58 flow temp most of the time.

I have 1 last question : how long should it take for the boiler to reach the desired flow target .