Underfloor with condensing oil boiler

Would only change if you're doing other house upgrades with grant. B3 isn't too bad, may just be something like open fireplace or old windows and doors.

We're in the same scenario. Can't get the grant for a heat pump because we're knocking all the walls. Was considering oil, but was told a buffer tank would be required for UFH? Would LPG make more sense over a 10 year period in a well insulated house? LPG is more expensive and has a lower energy density. But I wouldnt need to buy an oil tank or a buffer tank, might even swing a free oiler.... thoughts? I want a system that makes switching to a heat pump very straightforward in a few year.

We have done this on 1950's bungalow, Insulated the sh1t out of it UFH with mixing valve, MHRV, good windows doors. Stat connected to boiler set to 20 so house never drops below. Using approx 1,300-1,500 litres a year heating only.

Would a buffer tank make the system more efficient and save some oil?

Plumber fitted a top up valve to stop the mixer making noise. This is not working anymore and pressure is 0 but mixer doesn't seem to be making noise any more so does it matter?

A buffer tank would be unlikely to make a significant difference to the system efficiency. Certainly not sufficient to ever pay for itself.

Not sure why the mixing valve was making noise, or why this would be resolved by fitting what I am guessing is an automatic filling valve? If the water pressure is low that should be resolved before the thing overheats.

Often underfloor heating systems will require some form of hydraulic separation in order to work correctly. This could be provided in the form of a low loss header, or system link manifold.

The burner run time will be the same with either arrangement. A buffer tank will give rise to longer continuous running cycles vs more starting and stopping without. Much the same as with radiators.

He shouldn’t need any additional maintenance on his burner, it’s designed for constant stop/start operation based on the supplied duty stat differential.

If he has it serviced and correctly set up once a year it will be fine.

What return temperature is the (oil) boiler running at?, Grant and others stipulate a minimum of 40C?? to prevent corrosion so some form of bypass is required if running solely on UFH.

Suggest you look into that, I think that even though the condensing heat exchanger is stainless?, the main heat exchanger is mild steel and if the temperatures of the gases leaving the stainless HEX are too low then you can get corrosion in the main heat exchanger.