Boiler not reaching temp

[Jurassicspark]

Hi peeps.

Its winter and yes it is cold.
I see a lot of people are having issues with their heating at the moment which is not really nice.

I got a question.
Ok so, boiler set at 65 degrees with individual TRV's set at 18 degrees. Boiler fires up at normal at first and reaches 65 degrees in around 25 minutes. Then it drops to around 40 when boiler turns off the gas. It comes on again and reaches 60. After 2 or 3 times the boiler will then not heat up the water to 65 degrees, instead it will heat up to 45 degrees only and the radiators just become lukewarm... Is this a normal thing? My old boiler did not do this..... Its a Valliant boiler. Room thermostat still be calling for heat and boiler does this...


Please let me know
Thank you

 

[Johntheo5]

What model vaillant? How many rads?

 

[Jurassicspark]

What model vaillant? How many rads?

eco tec sustain it is.
14 rads.

 

[Johntheo5]

Should have asked the output of this boiler and if its a system (non combi) boiler.
Do you have TRVs (thermostatic rad valves) installed or/and are the rads zoned, is this problem arising with all 14 rads in service?.

 

[Jurassicspark]

Should have asked the output of this boiler and if its a system (non combi) boiler.
Do you have TRVs (thermostatic rad valves) installed or/and are the rads zoned, is this problem arising with all 14 rads in service?.

Its a combi boiler with 28kw output. I have trvs installed.

Boiler fires up to 65 degrees at first, then when the trvs hit room temperature the boiler only heats the water up to 45 degrees and maintains the temp.


Is this normal or not?
ty

 

[Johntheo5]

Its a combi boiler with 28kw output. I have trvs installed.

Boiler fires up to 65 degrees at first, then when the trvs hit room temperature the boiler only heats the water up to 45 degrees and maintains the temp.


Is this normal or not?
ty

No, certainly not normal IF the boiler is firing continuously, if the boiler is constantly/rapidly cycling then a different problem.

 

[fixitflav]

eco tec sustain it is.
14 rads.

Is it possible to set the maximum power in CH mode? If so, maybe it's set too low.

 

[Murdochcat]

Has anything been changed in the heating set up recently?

 

[fixitflav]

Has anything been changed in the heating set up recently?

Good question - is it a new house/new boiler/new problem or what?

 

[Jurassicspark]

Is it possible to set the maximum power in CH mode? If so, maybe it's set too low.

No, not possible to do.

 

[Jurassicspark]

Nothing been changed and setup still remains same from 10 years ago.
ty

 

[Johntheo5]

No, not possible to do.

It certainly is possible to range rate this boiler, like most Vaillants but I dont think thats the problem since it reaches the target temperature initially.

No, certainly not normal IF the boiler is firing continuously, if the boiler is constantly/rapidly cycling then a different problem.

Is the boiler cycling rapidly after the initial heat up?
you can look at d.40&d.41 flow/return temperatures and all sorts of useful info if you know how to access the d parameters, post a phot of the boiler front/controls and someone will show how to access them.

 

[Jurassicspark]

Is the boiler cycling rapidly after the initial heat up?
you can look at d.40&d.41 flow/return temperatures and all sorts of useful info if you know how to access the d parameters, post a phot of the boiler front/controls and someone will show how to access them.

At first it will heat up to 60 degrees and make the radiators toasty hot.. then the boiler will automatically shut its gas valve and drop the temp to 45 (room stat still calling for heat, so its a boiler setting) then it would go back to 60 degrees.. which is fine by me. After 2-3 attempts it then only heats to 45 degrees and stops there and it keeps the radiators lukewarm...

thanks for that, yeah i did see d.40 etc and it only showed flow, return temperatures but did not see any kw adjust setting... seen them before on previous valliants..

 

[Jurassicspark]

apparently i heard that the boiler sees the flow and return temperature the same (60 degrees) so it thinks that if the differential between flow and return was so low that the boiler says, ok, no heat is being lost .. thats why it does this

 

[Johntheo5]

At first it will heat up to 60 degrees and make the radiators toasty hot.. then the boiler will automatically shut its gas valve and drop the temp to 45 (room stat still calling for heat, so its a boiler setting) then it would go back to 60 degrees.. which is fine by me. After 2-3 attempts it then only heats to 45 degrees and stops there and it keeps the radiators lukewarm...

thanks for that, yeah i did see d.40 etc and it only showed flow, return temperatures but did not see any kw adjust setting... seen them before on previous valliants..

Are you saying it keeps firing (above) to maintain 45C or is cycling on/off which I think is what is happening.
I have attached a copy of a Vaillant Sustain below, if you look from page 46 onwards you will see all the d parameters, starting at d.00, maximumm heating output which defaults to Auto (full output) but can be set to any level you wish. If you scroll down (on the boiler menu), you should see d.40&d.41.