Combi Boiler function

BiliousGreen

Does a combi boiler burn gas in a binary or analogue manner? ie does it matter what its doing (analogue), or is on , on as such (binary)

If the boiler is on for an hour heating the house from cold to warm does it burn the same gas as it being on for 20 mins 3 times over a 2 hour period maintaining a temperature?

Are both hours of the boiler being on equal in terms of the gas burnt? 

Ie they are both an hour of the boiler being on, but do they both use the same amount of gas?? Assuming all else is essentially equal. Not sure if I have been thinking about this all the wrong way 

Neil_Jones

https://www.viessmann.co.uk/en/heating-advice/boilers/how-much-gas-does-a-boiler-use-per-hour.html - "It’s hard to give a precise figure to say how much gas your boiler should be using, however you can use the size of your boiler to work out an estimate. A 24 kW boiler will use 24 kW of energy per hour. If your boiler is on for a total of five hours per day, your daily usage should be around 120 kWh."

The boiler will use more gas initially to fire up, but once it starts ticking over (and is at temperature) it won't use anywhere near as much, but the true usage will depend on your settings, the outdoor temperatures, the insulation of the property, its size, etc.  If the thermostat doesn't have to keep clicking on and off to maintain a temperature, then your usage will fall.  If its freezing cold and you've left the door open (by accident or otherwise), don't be surprised if it does Duracell Bunny impressions.

TL;DR - too many variables.

macman

Modern boilers modulate down as the set temp is approached, rather than cutting out and in again. Same way that a gas hob flame can be made larger or smaller by turning it up or down.
The most gas will be consumed in the first hour from cold start-up, and will diminish as the house warms up.

BiliousGreen

Ah ok so I have been thinking about it wrong as such!! Thanks.

Once maintaining a given temp, the boiler seems to be on almost all the time. It will go off for 10 mins or so but then back on for 20. That 20 mins maintaining is not using the same gas as 20 of the mins used when heating the house from scratch. 
On time alone I was assuming I would be better off heating the house (2hrs) and then letting it go cold and then heating again (2hrs)  as the boiler would be on for less time than leaving it tick over almost constantly maintaining a temp. ie running for nearly 6 hours almost constantly in the evening 

BiliousGreen

So letting it run more frequently at the desired temp to maintain will likely be more efficient than letting it run for a similar time but having to heat the house from scratch each time as it wil modulate the gas used down as its only maintaining so 20 mins of being on will use a different amount of gas in each scenario. 

macman

The 'stat should switch the boiler off once it reaches the set temp. If it rapidly switches on again and struggles to maintain the set temp, then either the property is poorly insulated, or the system is undersized and having to run almost continually.

glennevis

BiliousGreen said:

Ah ok so I have been thinking about it wrong as such!! Thanks.

Once maintaining a given temp, the boiler seems to be on almost all the time. It will go off for 10 mins or so but then back on for 20. That 20 mins maintaining is not using the same gas as 20 of the mins used when heating the house from scratch. 
On time alone I was assuming I would be better off heating the house (2hrs) and then letting it go cold and then heating again (2hrs)  as the boiler would be on for less time than leaving it tick over almost constantly maintaining a temp. ie running for nearly 6 hours almost constantly in the evening 

If your boiler is running constantly it sounds like you don't have a room thermostat. First thing I added after moving into my present house was a room 'stat instead of switching the boiler on and off by hand every two hours. Best £10 I ever spent.

BiliousGreen

macman said:

The 'stat should switch the boiler off once it reaches the set temp. If it rapidly switches on again and struggles to maintain the set temp, then either the property is poorly insulated, or the system is undersized and having to run almost continually.

Could be either not sure, it doesnt stay off for long though, hence I have been turning it off at the stat and letting the house get cold over a few hours b4 turning it back on again rathet than having it run almost constantly. I dont notice any real drafts and its not a big house so the i-mini c30 should be enough. No idea how to tell

BiliousGreen

macman - After what you said I tried a little experiment, no idea if it was daft but .......
I allowed the boiler to heat house to 18 and then left it on controlled by the stat to keep house at 18. 

At about 45 min intervals I changed the flow rate on the boiler started at 60, then 69 (Eco), then 78, then dropped to 55 and tracked the fire times. In every instance the boiler basically went on for 5 mins and off for 5 mins to the point you could set your watch by it. Flow rate temp made no real difference, I thought hotter radiators may have kept house warmer for a bit longer when it went off but nope.

Is this telling me anything useful about settings or the boiler itself? Nothing meaningful changed during the time as we just watched tv whilst I did it so it was as fair real time as could be. 

Thanks

Ballymoney

I could be wrong here but your boiler may not need to hit the max flow temp to maintain your house at 18c. So raising it from 60 to 69 then 78 probably makes no difference if it only requires the system to tick over once the house is up to temp?

I could be completely wrong though.