Programmer - Heating Call Frequently Cycles

29 Aug 2011
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United Kingdom
I have a Drayton Digistat+3 programmer and I notice that it is designed to reach the desired room temperature by a very gradual process, and I wonder if that's a good thing.

As an example, suppose that the room temperature is 16 degrees and thermostat is set to 20 degrees. The programmer calls for the boiler to supply heat, which it does and all is good.

Now, when the temperature reaches about 18.5 - 19 degrees, the programmer will deactivate the call to the boiler, and the boiler will duly shut off, even though we are still short of the desired 20 degrees.

After perhaps 5 minutes or so, the programmer will again call for heat, this time for a shorter interval before then stopping the call. And repeat and repeat, with the boiler off intervals getting longer and the boiler on intervals getting shorter as the temperature gradually moves towards 20 degrees.

I wonder if this constant cycling is good for the longevity of the boiler? Is it energy efficient? Am I reasonable in wondering why the heating shuts off even though we're still so far from the target temperature?
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I wondered the same when I got new heating controls recently. It’s called TPI or chrono-proportional control. ( It is more efficient and should provide better comfort levels. Presumably the downside is additional wear on some components. However it is a very common feature these days so I would hope that boiler manufacturers design their products accordingly.
Most thermostats do this these days. The idea is to stop the room temperature overshooting the set point, and so save fuel. The general concept has been used in industry for decades particularly automated weighing systems, if for example, a large bakery can prevent going over on a few grams of ingredients for each weighed batch, over time it saves them a considerable amount of money in the long run.

Boilers always provide more heat than the sum of radiators they are connected to can dissipate, so to prevent the water actually boiling, they have to continually adjust the heat input to maintain the correct flow temperature anyway independently of the thermostat. Newer boilers will be continually modulating, and the older boilers that don't have flame modulation would frequently switch themselves on and off every 30 seconds or so to achieve the same thing.

Many components now state minimum life cycles in excess of a million operations, and in reality go on for much longer. Time will tell how boilers fare. The guys who regularly carry out repairs will soon start to notice if the component failure rate changes over time as the new technology is rolled out.

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