New boiler operation/settings

[John]

I recently had an old boiler replaced with a wall mount conventional (Ferroli Tempora - 100K BTU) on an S plan - pressurised CH, gravity HW. I did all the wiring myself and added a new cylinder stat and room stat. The boiler supplies approx 14 rads [mixture of old cast iron and new 'modern' rads] at the moment with 2 more planned. So far I`m impressed with the operation of the new boiler. The system heats up very quickly and I`ve checked operation of all the valves/stats successfully. What I`m concerned about is the following:

Particulary with the cold weather, I`ve noticed the boiler is on (firing) all the time during its programmed operation period (7.30am-9am, 5-9pm). The corgi who commisioned the boiler mentioned that the boiler wasn't operating near its full capacity (100k btu). I don`t know if the boiler modulates or not or if I have to change a setting on the board. There is a temperature setting on the front panel which is set to 70oC - is this too low? At the moment the house does get warm enough (assuming the boiler is firing all the time) but with the weather being colder - its not quite enough to trip the room stat off. If I change the output (BTU), will the boiler use more gas but operate for less time? - I`m not sure what I should be changing to get the optimum efficiency..

John

[BillR]

I would have thought 70C was too low. 80 would be more normal in a conventional system. However, often the temp is set to 70 as this is the point at which I believe scalding occurs, which may be an issue if you have young children. I wonder if the gas supply is sufficient for a boiler of this size to run at full capacity?

[John]

I think just over 80oC is the max setting on the boiler IIRC. What does altering this setting do inside the boiler? - does the water flow slower through the heat exchanger or does it burn more gas to achieve the higher temperature?

Gas supply is 22mm direct from the meter (approx 6m away). I`m pretty sure this is ok as the previous boiler was a similar capacity.

John

[Ed Sirett]

The boiler is almost certainly of a modulating type. The boiler control system will try to match demand and output. To heat the house more strongly you will need to turn the boiler up to a higher setting this will make the control system burn more gas and the rads hotter (injurous in fact).

I don't know if this has a seperate control for HW is so thee is no fear of scalding.

If the house is not getting hot enough in autumn with the rads as 80C you have a problem.

Are all the rads bled (i.e. no cold tops on the rads?). Are any TRVs turned up enough (halfway should be enough to be comfortable). Are any stuck? Is all the house cold or just parts?

Note October is a hazardous month for heating engineers - customers complain as the house cools down from summer temperatures to winter temperatures. 20C can feel quite cold in October yet comfortable in January.

My rule of thumb [another one that will make the book-wise and half-educated cringe] is that you need 2kW per radiator. This means in a

14 rad establishment will need a 28kW boiler - you are on the limit on that one so it is just possible that you needed a bigger boiler? Suggest draught proofing and insulation.