Plumbing – Does the boiler try to heat water in the tank if it’s already hot

combiheatingplumbingwater-heater

I've got a combi boiler which heats the hot water tank using the indirect method. I use Hive to control it.

I'm trying to work out: if the hot water is set to on for an hour, will the boiler constantly heat the hot water tank for the entire hour, or will it detect when the water is hot and then turn off? and in like manner, if it is set to come on, and the tank is sufficiently hot from a previous slot in the schedule, will it still try and heat the tank?

Just trying to work out the best schedule and can't find an answer to this anywhere…

From a comment by the OP:

I'm trying to set up an efficient Hive hot water schedule, to give me hot water when I need it. In Hive hot water settings you can set to on/off only, believe temp control is managed by the tank… (don't have the models of tank / boiler to hand). So I wanted to know if I set the Hive schedule to On several times a day, whether it would burn gas still even if the water is already hot. I was guessing there's a temp cutoff, but wanted confirmation as I couldn't find any useful info about it elsewhere.

Best Answer

If the water is still hot enough, the control system would not start reheating it. There is a hysteresis involved.

Explosions should never be a problem, if safety standards are followed. The redundant devices are:

  1. Safety thermostat which interrupts the energy input (switch for electric systems or oil burners, valves for gas) at a level below 100 degree Celsius.
  2. The control thermostat which is used by the control system - it must be completely independent of No. 1
  3. A safety pressure relief valve that opens the boiler water line if a high pressure is detected, f.e. 300 kPascal.
  4. Also a safety issue: The Legionella problem should be considered, i.e. once a while the complete hot water system should be heated up to at least 60-70 degree Celsius and all hot water faucets should be run for a minute.
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