Pipework advice - Central Heating System

[ShaunCorbs]

What boiler is it ?

 

[Desktop987456]

It is non condensing locally made boiler as I am not in UK.
The return lines of the extended section (old pipwork) has lost some of the insulation material and is exposed to outside temperature, does it affect how long the burner is on?

 

[Desktop987456]

Increase in gas use sounds about right doesn't it? To improve efficicency and therefore consume less gas lower the flow temp as much as possible to be comfortable which will also increase burn time but at a lesser gas rate.

Do not move the sensor.

Thanks for your comments. The sensor was slightly off from the pipe which wasn't give accurate reading. Now sorted the sensor and gas usage on hourly basis is 1.1 units per hour which was just about what I expected after extended pipework and radiators. Thanks for everyone's help.