Boiler adjusting max useful heat output

[dilalio]

 

[GoodDIYjob]

Yes, looking at my scribbles I have made a mistake there. Good pickup.


I'll try to do the gas rate measure tomorrow morning during the 2:30 on cycles..

Thanks again. I know more than when I started...

Ok, so hopefully some clarity now.

Today, after initial warm up to flow temp. The boiler was 2minutes firing, 3 minutes rest (pump running).

The outside temp was a lot higher, and as a result the room temp was already at 17.5c after 20 mins. Some of the upstairs TRVs may have already closed causing the change from 2:30 on 2:30 off over previous days. I make 2:3min ratio using 40% of min modulation, so about 5.2kw.

For gas readings, I turned the CM927 up to 22C, so it wasn't approaching TPI range (as it was pretty much already there today).

The Gas use was between 1.61 and 1.63m3 per hour. The manual specification says min 1.64m3.

This was timed for the full firing duration of 2 min (first one: 3min after initial heatup). What I did notice, is if I just time the first 30 seconds, the gas use was higher, as the meter is spinning faster for the firs few seconds (ignition pressure?). Worked out to the 1.68M3 for first 30 seconds. A figure I often see if I time a short duration in CH operation.

Data below, this post in attachment.

So my interpretation of where things are at. Please correct if I am off track.

• Both rad output and heat demand from house are materially lower than minimum modulaiton of the boiler.
• We could do with a new boiler which modulates down to 6 or 7 kw.
• We could do with some more heat output. Maybe add in kitchen, a new rad under main lounge window, upgrade bathroom emitter.
• Gas use during the firing cycles seems to be within the minimum gas use range, so doesn't seem a lot of point paying for an engineer to adjust the CH max output, although it may shave a little bit of initial heat surge off the cycles.
• I also did a quick check on degree days, 16C base temp, based on a heatloss of about 8.5kw for a 21C delta and it reconciled quite closely to my annual gas use (about 10,000kwh if I take off 3,500 est. for DHW), so I think we are in the ball park, in the ranges discussed.

Thanks for the responses and in depth critique.