by ericmark »
Mon Feb 04, 2019 9:35 pm
In the main the pump, by-pass valve and heat exchanger are all built into the boiler.
Oil and solid fuel are different to gas, but don't think oil and solid fuel had condensing boilers 20 years ago, so assume gas.
So first thing is to consider how the central heating works, in order to get the moisture in the flue gases to condense you have to limit the temperature of the return water, to do that, it has to modulate (turn down output) so in turn all the controls have to also turn up and down not off/on.