I was once asked to look at a device that had been retrofitted to an oil boiler heating a swimming pool.
The device had been sold as a fuel saver for what seemed like a lot of money at the time, I think it was something like £200 (around 23 years ago). The owner reconed it had paid for itself in the first year and was very keen for me to fix it as it had stopped working.
This £200 box contained a small hand soldered board with a 555 timer switching a relay. The fault turned out to be a failed relay so was an easy fix.
The device worked by delaying the startup of the burner when the thermostat called for heat, there was a pot on the fromt of the box labeled low to high saving. The higher the saving selected the longer the delay before starting the burner. I think it was something like 20 to 30 mins delay.
This delay has the effect of increasing boiler run times by forcing longer off periods.
I have no idea how well this works in a domestic application, it's on my to do list to try with my heat pump.
Steve
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