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
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
I would have thought 70C was too low. 80 would be more normal in a
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
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
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.
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
I don't know if this has a seperate control for HW is so thee is no fear
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
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.
Ed Sirett - Property maintainer and registered gas fitter.
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