Boiler firing timings

Reed_Richards

There are two types of boiler control using a room thermostat:

1. The boiler knows what the room temperature and the set temperature is.
2. The boiler just gets an on/off signal from the room thermostat.

With the first type of control the boiler may well be able to keep going by modulating down to the output necessary to maintain a constant room temperature.

With the second type of control the boiler is much more likely to cycle on and off. 

 

markin

It likely modulates down to around 7kwh, 3.5kwh for the 30min it actually runs when modulating  Vs the 24kwh (12kwh for 30min?) from a cold start. So off for 3hrs would save 10.8kwh but then maybe cost that and an extra 1.2 to get it back up?

Just measure the gas usage with a constant outdoor temp.

tghe-retford

I just did this myself with my Baxi boiler out of curiosity. So while I remember the numbers:

63°C flow rate - 1:47 on, 3:00 off.
58°C flow rate - 1:24 on, 3:00 off.

For both, it's taking about 8-10 minutes to warm up.

I did this because of a Daily Mail yesterday article suggesting that it costs £2.40 an hour to run a 24kW boiler at 10p per kWh.

[Deleted User]

I did this because of a Daily Mail yesterday article suggesting that it costs £2.40 an hour to run a 24kW boiler at 10p per kWh.

Write this down as your first New Year’s Resolution: Don’t believe everything that you read in The Daily Mail.

I have a 24kW system boiler that comes on at 6.45am with a max flow temperature of 55C. Note the total usage in the first 45 minutes yesterday was about 12kWh and 16kWh in the first 1hr 15mins. (Stats from a smart meter as recorded by BRIGHT app).

tghe-retford

[Deleted User] said:

I did this because of a Daily Mail yesterday article suggesting that it costs £2.40 an hour to run a 24kW boiler at 10p per kWh.

Write this down as your first New Year’s Resolution: Don’t believe everything that you read in The Daily Mail.

I have a 24kW system boiler that comes on at 6.45am with a max flow temperature of 55C. Note the total usage in the first 45 minutes yesterday was about 12kWh and 16kWh in the first 1hr 15mins. (Stats from a smart meter as recorded by BRIGHT app).

The second I saw that claim, I was instantly sceptical and thinking of a word that is synomous with 'nonsense'. I know from my own observations that the boiler does not constantly use 24kW. Alas, I can't check now as I no longer have a smart meter but when I had one, it started at 24kW for a few minutes before going down to 9-11kW when it was on and 0.5kW when moderating.

By logic alone, what would be the point of turning down your boiler's flow rate and having a condensing boiler if it costs £2.40 an hour regardless of what you do? It makes no logical sense.

It is irresponsible for them to make that claim that will panic people into thinking they're paying more for gas than they actually are. Or worse still, have people assume that it's pointless to run their boiler at less than maximum settings because they assume they won't save money as a result of reading said article.

BiliousGreen

So based on those stats you guys wouldnt worry about the boiler doing 6mins on, 4 mins off for hours at a time to maintain a temperature at a flow rate of 55 Degrees?

[Deleted User]

BiliousGreen said:

So based on those stats you guys wouldnt worry about the boiler doing 6mins on, 4 mins off for hours at a time to maintain a temperature at a flow rate of 55 Degrees?

Make your own mind up. It depends on the type of boiler that you have. Most gas boilers are on a 6 cycle + 1 minute on time/per hour set up:

https://www.heatgeek.com/what-is-boiler-modulation/

I should add that turning off radiators effectively leaves you with an over-sized boiler.

Astria

BiliousGreen said:

So based on those stats you guys wouldnt worry about the boiler doing 6mins on, 4 mins off for hours at a time to maintain a temperature at a flow rate of 55 Degrees?

Personally I prefer boiler on for 15 minutes, off for 10 minutes as I consider the boiler firing more than 3 times an hour to be excessive, but if you don't mind the additional wear and tear on the boiler components heating up/cooling down then it's fine. It's all personal preference.

If your boiler is oversized (or radiators are turned off), then it will not be able to modulate down as far, so will typically trip out earlier.

grn99

Astria said:

BiliousGreen said:

So based on those stats you guys wouldnt worry about the boiler doing 6mins on, 4 mins off for hours at a time to maintain a temperature at a flow rate of 55 Degrees?

Personally I prefer boiler on for 15 minutes, off for 10 minutes as I consider the boiler firing more than 3 times an hour to be excessive, but if you don't mind the additional wear and tear on the boiler components heating up/cooling down then it's fine. It's all personal preference.

If your boiler is oversized (or radiators are turned off), then it will not be able to modulate down as far, so will typically trip out earlier.

Agree with this. I've set my wiser to "oil" as the fuel as that changes the TPI to 3 cycles an hr rather than 6 given what the boiler has to go through at each startup when heat is called for.

Olly_J

grn99 said:

Agree with this. I've set my wiser to "oil" as the fuel as that changes the TPI to 3 cycles an hr rather than 6 given what the boiler has to go through at each startup when heat is called for.

   +1 for this, I found my Wiser was conflicting with the anti-cycle timer on my Valiant Ecotec on the 'gas boiler' setting, having it set to Oil fixes it