ARW wrote:
On 15/05/2021 11:27, Theo wrote:

I never investigated but I imagine there was just on/off control for the
boiler (gas valve only, since there was an always-on pilot that had a piezo
spark-button to relight it if it went out), and an additional time clock
output that was in series with a thermostat to run the pump for the heating.

How was the boiler turned off in this system, when the thermostat said the
house was hot enough and so was the water? If the heating called for heat
and the hot water was up to temp, surely that would overheat the water?

https://assets.danfoss.com/documents...6en-GB0201.pdf

Were the common programmers of the time

This was the one:
https://www.amazon.co.uk/LANDIS-GYR-.../dp/B072FSJP2N
which was just a simple 1 rev per day motorised dial plus some cams to
operate switches.

Being on gravity makes a lot of sense - the neighbours moved their cast iron
boiler into the garage and 'it never worked properly after'. Which would
follow if the tank is suddenly further away from the boiler.

Theo