Quote:
Originally Posted by thenry
[That's what I thought but these things are not accurate according to qualified people so I've learnt to live with the whooping 5 degree difference
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Older central heating is affected by 2 forms of hysteresis.
The first is when the thermostat cuts off the heating when it reaches the desired temperature, but the hot water in the radiator continues to warm the room.
The second is due to mechanical thermostats having a lag between their on and off conditions. This can get worse over time as internal springs and magnets become less effective.
A cheap electronic thermostat overcomes this due to it using a thermocouple.