"Andy Hall" wrote in message
...

I found it to be poor on the old system
because it was a long time
before the boiler would come on, by
which time a lot of water had been
used. Then the temperature would
overshoot by a long way and the
water too hot during later use.

The simplest method to re-heat a cylinder. Have two cylinder stats, top and
bottom of the cylinder either strap-on or immersed. Immersed is better, but
not that crucial. Have the bottom stat set to 60C for Legionella problems,
the top, about 1/4 of the way down and set to just below the desired DHW
temp you want. Have a DHW blending valve on hot draw-off pipe, which are to
become mandatory. Set this to your desired DHW temperature, say 50C. DHW
is then user adjustable.

When the cylinder is up to temp at 60C the bottom stat cut out the boiler.
When the temp get below say 48C, the top stat will bring the boiler in when
the temp is below say 47-48C. The boiler heats the cylinder with one long
burn and no inefficient boiler cycling.

If the cylinder is running out of hot water too quickly, then there are
three options:

1. Raise the bottom stat temperature to give more stored hot water, say up
to 65 to 70C. The DHW blending valve will ensure the draw-off temperature
is what the user wants.

2. Insert a flow switch into the pipework just before the high flow taps
(bath and shower), and install a third high limit cylinder stat, set to 80C.
The flow switch will bring in the boiler immediately heating the DHW
cylinder preventing the bottom of the cylinder being very cold with entering
cold water before the boiler cuts in.

3. Do both 1 and 3 above.

Doing the above effectively increases the size of your cylinder. Quite
simple and easy to do. Many people when installing full lengthy body jets
have a larger cylinder installed. This in many cases is unnecessary. The
above could be done and money saved in boiler efficiency.