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Heating engineer and electrical engineer fitted Aztec 6KW electric heater.
When in use this heater sounds like a "Quick-boil Kettle"coming to the boil and when it shuts off it just starts up again within 20 secs, heats for 20secs. then stops again. This start/stop cycle is continuous. When "off the amber lamp flashes and is steady when "on". The red light does not show.
All rads. are fitted with thermostats and work perfectly well. The pump, bypass,return and flow circuit around the boiler get to hot to hold your hand on but the flow and return get cooler towards the floor with no excessive heat at any rad. including the open one in the toilet .With the frost lately this is proving expensive while the noise is very disturbing. Any advise on how to sort this will be very much appreciate. Thanks in advance for your time.

Hi,
the fact the bypass circuit gets hot says it may be bypassing when it shouldn't be, ie water going straight round short loop instead of whole system. Is it a proper automatic bypass valve which stays shut until last TRV shuts off or is it just a cheap-skate gate valve, half shut?
See ARV22 for example of correct type, which complies with building regs Part-L for energy efficiency.
This is the the valve refered to on page 7 of the install manual under the flow rate chart,
regards