Correct boiler setting

[ALEC1]

Generally that's true though... You have installed and commissioned a hybrid system that does something different...there is also one documentation saying that on/off controls mixed with a compensated flow temp is even more efficient..but the balance has to sought between burning gas efficiently and the negative effects of short cycling... Unburnt gases and fan cooling of the hex... It's why long burn times are preferred, and TPI through a relay as opposed to lowering the flow temp may just rob Peter to pay Paul in the efficiency search...

 

[jpm777]

Try lowering the P:b setting.


Have you measured the waste of gas? Otherwise it is subjective.

Hi Dan,

the Pb is set to 1.5 which is as low as it goes.

I have done multiple tests on comparative consecutive days (temperature wise) and the days I left the stat at a fixed temperature (and the boiler cycling on/off due to the stat) it used considerably more gas.

This backed up what I was expecting given that when the heating was off for an hour or sometimes even a few hours, the actual room temp on the stat did not change - thus no gas usage for a given temp versus the boiler on and off multiple times within that given period and cold radiators throughout.

It would seem from posts that perhaps the system is flawed with the way it interacts either due to design or its interaction with my non condensing boiler.

It is a shame as I had hoped that a big brand name like Honeywell product, that claims to be very energy efficient would work in practice. Maybe it is just the fact that my boiler is non condensing. If this is the case it should be mentioned in their literature as to suitability.

I guess I will have to change the stat at additional cost so as to avoid the higher running costs and wear and tear on my boiler.

Thank you Dan, and everybody for their replies.

JPM777

 

[Dan Robinson]

Just about to crash.... and when I said lower - my brain hadn't fully kicked in due to being the morning - and driving. The joys of the season.


Anyway - try raising the P:b setting to 3.

TPi I admit is flawed - but on modulating burners. With on/off boilers such as yours the theory is sound and should work. Ironically the only WB CBi boiler i have seen die from the small boilers equivalent of back end rot had the most basic of on/off controls and no anticipator connected to the room stat.


Is your house very well insulated?

Ignore the little debate between Alec and I - we have a strange mix of conflicting and agreeing views on control systems that are irrelevant to 90% of the UK population. But he does try and get BUS and compensated controls into every sentence he speaks/types .

 

[jpm777]

Just about to crash.... and when I said lower - my brain hadn't fully kicked in due to being the morning - and driving. The joys of the season.


Anyway - try raising the P:b setting to 3.

TPi I admit is flawed - but on modulating burners. With on/off boilers such as yours the theory is sound and should work. Ironically the only WB CBi boiler i have seen die from the small boilers equivalent of back end rot had the most basic of on/off controls and no anticipator connected to the room stat.


Is your house very well insulated?

Ignore the little debate between Alec and I - we have a strange mix of conflicting and agreeing views on control systems that are irrelevant to 90% of the UK population. But he does try and get BUS and compensated controls into every sentence he speaks/types .

Hi Dan,

Thanks I'll try raising it to 3 and see what happens.

I had put it on 1.5 so that when trying to achieve a higher temperature it continued to give 100% until 1.5c before the set point to heat the house up quicker.

My house is well insulated, having been constructed in 2005, with the Pb on 1.5, I experience 0.5c (normally) to 1.0c (occasionally) of overshoot and have just adjusted the set point accordingly.

 

[Dan Robinson]

Getting the setpoint right is vital and because it is such a precise device positioning is also key.

Raising the pub might help but you might lose some comfort.

I'm wondering if having really good insulation has flummoxed it somewhat.

Your house builders were obviously cutting corners with that boiler as it should have been a condensing model. They got away with it due to when the planning application went through.

 

[ALEC1]

given that an awful lot of condensing boilers ignite on full output and then wind down, the whole concept of calling for the boiler for a small amount of heat is deeply flawed..as the boiler will inevitably fire at full output.

This is a typical example as to how a manufacturer pulls the wool over everyones eyes on the back of a good reputation...and should concern all of us consumers and installers...remember rip off Britain... its still here..lock stock and barrel!

 

[Dan Robinson]

What boilers fire at full rate?

All the ones I deal with fire at a given % to confirm ignition then ramp down.

Unless in hot water mode of course.

 

[ALEC1]

Vaillant and Viessmann both fire at full rate then ramp down according to range rating or demanded temperature....

May be Vaillant fires at 70%, though.

 

[David937]

Vaillant and Viessmann both fire at full rate then ramp down according to range rating or demanded temperature....

May be Vaillant fires at 70%, though.

From my observations on my 2008 Vaillant Ecotec, it doesn't start at full rate, it starts at minimum rate and then increases to full rate after a minute or so. I have a VRC430f and if that calls for a low flow temperature it won't even ramp up to full rate unless the system has cooled down significantly. I believe the 400 series are different though.

However when I had a Honeywell CM907 and the flow temperature was just left set at ~ 70ºc, it would receive a call for heat, fire at minimum rate, increase to full rate after a minute (to achieve the flow temperature of 70ºc) but then the stat would stop calling for heat so it would turn off again. This might be why Dan said TPi is flawed on modulating burners? Or I could be missing the point completely

 

[mogget]

The Vaillant 418 starts at about 70% for about a minute before modulating up or down as necessary. Unfortunately this can lead to short cycling on low loads.

The 615 starts at maximum rate for a few seconds only, then ramps down to minimum before slowly modulating up. This works much better!

So even with the same manufacturer there is considerable variation.

Edit: for manufacturer read badge

 

[jpm777]

Getting the setpoint right is vital and because it is such a precise device positioning is also key.

Raising the pub might help but you might lose some comfort.

I'm wondering if having really good insulation has flummoxed it somewhat.

Your house builders were obviously cutting corners with that boiler as it should have been a condensing model. They got away with it due to when the planning application went through.

In terms of location, the stat is in the hall and I have taken all steps I can to ensure there is no draught through the wall cavity or from the front door to interfere with it working correctly.

I've now adjusted the Pb to 3 and it may be a little better, but too soon to tell. I'm on nights at the moment (thus the timing of my posts!), but will check to see how it is behaving in the next few days. Does this stat 'learn' the thermal properties of the house via some type of fuzzy logic? IF so, I guess it may take a few days to settle anyhow.

About the boiler, yes the builder definitely cut corners.

I have already questioned this with them. The planning permission was approved in 2004 and when I asked about the boiler regulations since April 2005, they explained that they had bought a lot of old stock, and so as they were purchased previously that they were allowed to use them within a reasonable time.....

 

[jpm777]

given that an awful lot of condensing boilers ignite on full output and then wind down, the whole concept of calling for the boiler for a small amount of heat is deeply flawed..as the boiler will inevitably fire at full output.

This is a typical example as to how a manufacturer pulls the wool over everyones eyes on the back of a good reputation...and should concern all of us consumers and installers...remember rip off Britain... its still here..lock stock and barrel!

All too true it would appear!

 

[Dan Robinson]

The dt90e isn't intelligent in that way - the cm921 and 927 are.

If you work shifts or have a very irregular life pattern then stick with what you have.

 

[jpm777]

The dt90e isn't intelligent in that way - the cm921 and 927 are.

If you work shifts or have a very irregular life pattern then stick with what you have.

Cheers Dan, I'll persevere with it a bit longer.

I work shifts, but my wife is home most of the time with young kids.

If I do change it I'll just buy a basic digital stat with no TPI or the equivalent thereof.

I'm interested to see if the pb on 3 will help, so will see how it goes. It would be nice to be able to set the stat on a constant set point all day without the boiler constantly needlessly firing. Recently to save this waste and wear and tear, I had been controlling it just using the green boost button.