Managing boiler settings

[someonelse]

The set-up is
* conventional oil boiler
* hot tank in airing cupboard
* 3 port diverter & pump in airing cupboard
* heating managed by wireless digistat (receiver in airing cupboard)

The 'problem' (if it IS a problem) is the boiler frequently firing up/switching off. It runs for 3-5 minutes. I've heard this can be an inefficient way to run, as well as wearing out parts. True?

With the weather as it is:
* the digistat is calling for heat pretty well constantly
* so digistat shows 'flame' calling for heat &
* receiver shows green (receiving the heat call) &
* the pump is running (constant)
* but the boiler is still switching on & off.

At present the boiler temp setting is near maximum. (Lower level settings and the rads don't really get hot). My guess is that the water temp is reaching that set on the boiler, so boiler goes off, but as Digistat still calling for heat, the pump keeps going. Am I right so far?

If I turn the boiler down, will it run more efficiently? (though rads will be less hot)?

If I turn it fractionally up (to full), will THAT make it more efficient?

Any comments?

Cheers!

 

[Agile]

Oil boilers in domestic sizes dont usually modulate so they run at full power all the time.

When the set flow temperature is reached they turn off until it falls and more heat is needed.

Tony

 

[david3456]

The 'problem' (if it IS a problem) is the boiler frequently firing up/switching off. It runs for 3-5 minutes. I've heard this can be an inefficient way to run, as well as wearing out parts. True?

What boiler have you got?

At the moment I am monitoring my boiler (a Baxi Solo) to see what tweaks I can make. I have two boxes each with two probes for recording temperature, one on the boiler and another that I move round the radiators.

I find the 3 minute cycles very annoying too but it just seems to be the way it works. Here is a sample showing flow, return and difference.

https://docs.google.com/file/d/0B4xffi9ItIebWGpNQWhXLWh0STQ/edit

The top chart covers from about 4:30 in the afternoon to about 11:00 the next day. The bottom chart is just an expansion of the morning burn.

Basically, when I bought the boiler, 15kW seemed to be the recommended size for the house (4 bed detached) when 9kW would have been more suitable. So it can only burn for half the time.

 

[Agile]

To the OP, if your boiler is off for more than about 40% of the time then ask your engineer when its next serviced if its possible to reduce the power input a little then it will extend the "ON" period and shorten the "OFF" period.

Tony

 

[david3456]

The set-up is
* conventional oil boiler

Ah, didn't notice that to begin with

 

[Agile]

When writing exams and also on forums it pays dividends to read the question properly first!

 

[someonelse]

Wow! Didn't expect replies till tomorrow - don't boiler techies sleep?!

Many thanks all.

Just to clarify/expand, it is a non-condensing (installed a year before they became compulsory) 'Turco 2000 70/90' (also known as 'Eurocal' I think).

Oil boilers in domestic sizes dont usually modulate so they run at full power all the time.

When the set flow temperature is reached they turn off until it falls and more heat is needed.

'modulate' = switch on/off yes?
'set flow temp' = woter temp set at boiler, or room stat setting?(sorry to be dumb!)

To the OP, if your boiler is off for more than about 40% of the time then ask your engineer when its next serviced if its possible to reduce the power input a little then it will extend the "ON" period and shorten the "OFF" period.

Ah! Is this to do with the '70/90' bit? I always wondered... so the initial installation of the boiler has a variable range of power outputs...?

 

[D_Hailsham]

1. 'modulate' = switch on/off yes?
2. 'set flow temp' = woter temp set at boiler, or room stat setting?

1. No!
2. The flow temp is the water temperature set at the boiler.

A modulating boiler is one which can automatically vary its output between a lower limit and an upper limit, e.g 5kW to 20kW; they are normally controlled by the flow temperature. So when the water is cold the boiler will run at full output until the set temperature is reached. Then, instead of turning off, the output is reduced to maintain the same flow temperature. If the boiler reaches the lower limit but the flow temperature continues to rise above the set value, the boiler will switch off and wait until the temperature has dropped below the set value. It then turns on again and the cycle start again.

Problems usually occur because the boiler cannot modulate low enough, particularly in the milder weather when less heating is required. This occurs frequently with combi boilers which are normally sized on the hot water requirement, without taking the heating requirement into account.

Modulating oil boiler are not available in the UK. This is because the price would be prohibitive.

 

[snb]

your current oil boiler can have it's out put reduced. it needs to be re jetted and have the combustion setup.

best is to get an oftec engineer to come and reduce the output

 

[someonelse]

Once again, many thanks.

I'll get my OFTEC guy to do this when he comes for the summer service, unless you think I'm likely to be actually causing damage...?

edit: Just done some timing:

ON: 2.5 minutes
OFF: 2 minutes
ON: 4 minutes
OFF: 2.5 minutes
ON: 4.5 minutes
OFF: 2 minutes
ON: 3.5 minutes

 

[someonelse]

Just had an answer from the manufacturer's technical adviser:

Your Boiler is working fine exactly how it should.

So all seems well!

 

[Agile]

Hmme....

Your boiler is obviously significantly oversized because in this generally cold weather ( 0 C to 6 C daytime ) its not needing to run for more than about half the time!

Whilst its operating correctly for the set power output, it would be somewhat more efficient if it ran for most of the time.

You dont bother to say in your profile where you are so I cannot specifically advise for your exact location, but about 30%-40% power output might be appropriate.

Tony

 

[scoobydo123]

Possibly relevant what stat do you have?

 

[someonelse]

Hmme....

Your boiler is obviously significantly oversized because in this generally cold weather ( 0 C to 6 C daytime ) its not needing to run for more than about half the time!

Whilst its operating correctly for the set power output, it would be somewhat more efficient if it ran for most of the time.

You dont bother to say in your profile where you are so I cannot specifically advise for your exact location, but about 30%-40% power output might be appropriate.

Tony

Sorry. Didn't bother as didn't think it would be relevant. Midlands.

Short of changing the boiler, how can I reduce output? If at all.

Possibly relevant what stat do you have?

Drayton Digistat RF2

 

[scoobydo123]

Doesn't look like the stat offers any TPi control so dont worry about the Stat.