Time taken for unvented cylinder to get back to temperature

[Ackoman]

Hello,

In my previous house, the hot water was supplied by a combi boiler and so, fairly obviously, when having a shower the gas was burning for exactly the same length of time that I showered for.

In my new house, we have a system boiler which heats up an unvented hot water cylinder. If I shower for e.g. 10 mins, the boiler runs for approx 20 mins AFTER I'VE FINISHED SHOWERING before the thermostat switches it off again.

Why should this be? Are system boilers less "oomphy" than combi boilers? I'm using approx the same amount of hot water now when I shower compared to my old house, so why does it take twice as long to replenish it?

Thanks,
Ackoman

 

[cross thread]

the boiler will be switching on/off during that period as it raises the tank temp,so the pump may be running but the burner will not

 

[Ackoman]

the boiler will be switching on/off during that period as it raises the tank temp,so the pump may be running but the burner will not

Ahh ok, that makes sense - thanks!

 

[JohnD]

I notice that my neighbour's combi boilers seem to run flat out during a shower, whereas mine modulates down (reduces the flame size) unless the cylinder is completely cold, because the heat-transference capacity of the coil is not able to absorb all the heat the boiler can produce. Mine is much quieter and does not produce a vast cloud of steam on a frosty morning. I have a blue cylinder so will presumably have a smaller coil than yours. Also the boiler is lower power than would be needed with a combi.

 

[muggles]

System boilers do tend to be much less powerful than combi boilers, could even be half the power. You'll probably find you're using more water with the unvented too