Central Heating not reaching set temperature

[palmer1986]

Hi,

Can anyone answer this question before i call out a plumber.

I have a 'Vaillant ecoTEC Plus 425 Combi Boiler' it was installed about 9months ago, for the past 9months the central heating and hot water have worked perfectly.
Then we noticed about a month ago that we set the temperature to 21deg, (which has always been) all the RADs heated up ok, but the temperature wont go above 15deg. But before would heat up ok at 21deg within about 2-3 hours.
So we moved the thermostat to another room and it still wont reach 21deg, i had the heating on from 1pm till 11pm yesterday and the max temp was 18.5 deg!
Any ideas?

 

[RigidRaider]

'Ere we go again.... how good is the insulation in your attic? What depth?

 

[YELLERBELLY]

what programmer have you got? btw you aint got a 425 combi

 

[palmer1986]

Thanks for replying.

The correct boiler i have is a 'Vaillant EcoTEC plus 24'

The insulation is my loft looks about 20 years old and needs replacing, i would say the depth is about 1-2in.
I can see were your going with this, but my old boiler which was about 30 years old worked fine last Winter.

The programmer i have is a 'Vaillant VRT 360f' (its wireless)

The mail point i am try to figure out is if i set a temperature (lets say 21deg) the heating system should push more heat out to reach that heat (should it?)

 

[stem]

The main point I am trying to figure out is if I set a temperature (lets say 21deg) the heating system should push more heat out to reach that heat (should it?)

Not if your house is loosing heat as fast as you can pump it in. Try filling a bucket with water when there's a hole in it. You can leave the tap running forever, but it will never fill. If it's 18 degrees indoors and -8 outside today that's a massive 26 degree differential. With poor insulation, the bigger the differential (hole in the bucket) the worse the problem.

The question is, are the radiators hot to the touch? If so, then the heating system is supplying as much heat as it can, & can probably do no more. If the radiators aren't hot then there's reason to look elsewhere.

 

[pooch251081]

Agree with above comment, been looking at similar issues in the last few weeks as we just installed a room thermostat and as the weather has dropped, at my old setting (about halfway on the boiler CH thermostat) the room would never get up past 18.5 no matter how much higher you set the room thermostat. We have an old 1920s bungalow with bi-layer concrete walls and an unfilled cavity as well as suspended timber floor so despite just having had 250mm roof insulation installed, we will always suffer a great deal of heat loss in the winter and I have had to turn my boiler setting up to three quarters of max output now to reach 20. Have you turned your CH up to max just to see if that helps it reach temp? Are your rads as hot as usual? If they are colder at the bottom, they may need a flush to allow full flow throughout.

 

[palmer1986]

To: stem

Thanks for the reply, I agree the insulation is currently poor in the loft, and i understand what you mean, but as i have stated, last winter i had a 30 year old boiler and it was hitting 21deg fine.

The RADs are steaming hot, so it does look like its pushing the max, i just dont get why the old boiler was hitting 21deg and this new one isnt.

 

[stem]

Was it this cold last winter where you are? It certainly wasn't anywhere near as cold where I am.

The boiler will deliver hot water to the radiators at the temperature you set at the boiler thermostat, & I assume you've checked that. There is a safety maximum otherwise you could get serious burns from the radiators if you touched them. If the radiators are hot the boiler is doing it's job.

I doubt the radiators were hotter to the touch with the old boiler?

Anything changed since last year? Have you installed a big set of patio doors, or disturbed the loft insulation? for example.

Sorry about the edits, must use the spell check first

 

[pooch251081]

I'm pretty sure this definitely has something to do with the sudden drop in temperature, its reaching near -4 in some areas at the moment, even my new greenstar 37CDi (almost too powerful for my current system) is taking a bit longer to reach room temp. I would strongly recommend turning all your TRVs to max, and the CH thermostat to max and then monitor the room temp, see if it reaches max.

 

[D_Hailsham]

The correct boiler i have is a 'Vaillant EcoTEC plus 24'

Is it the 624 System boiler (You will have a HW cylinder) or the 824 Combi boiler (NO HW cylinder)?

The insulation is my loft looks about 20 years old and needs replacing, i would say the depth is about 1-2in.
I can see were your going with this, but my old boiler which was about 30 years old worked fine last Winter.

Current recommendation is 270mm. You can get very good deals on Loft and cavity insulation. Check out Energy Savings Trust Grant Search

What make/model was your 30 year old boiler?

Did your installer recommend the boiler and did he do a Boiler Sizing Calculation?