how long for water to heat up

thelawnet

I have a Potterton profle 50 NG boiler. Heating output is around 12kW.

I have an insulated tank that seems to be around 120l. I also have about a 12 panels worth of radiator.

It seems cold water is coming into the system at 10C. The temperature is set quite low on the boiler thermostat and hot water seems to be about 45C.

There is also a 3kW immersion heater on the water tank.

If I use up the hot water, how long should it take for the gas to heat it up again?

coffeehound

As a ballpark figure, this calculator:

http://processheatingservices.com/water-heating-time-calculator/

suggests 25 minutes. That assumes the water is all at 10C and that the boiler is supplying 12 kW continuously to the cylinder’s heating coil. In reality, it won’t be that efficient.

Rodders53

Hot water stored should be regularly (min once per week) heated to 60C to prevent legionella. While not mandatory in homes (unlike in other buildings) I'd not want to risk it for me and my family.

Either use the immersion heater (via it's own thermostat) weekly or increase the boiler temp and tank stat for every day. {That may increase running costs a little.