Replacing W plan timer

[jackrussel]

Greetings everyone.

I am looking to replace a timer controlling a w plan system of 1974
vintage.
The original specified timer had a heating proirity switch. Does anyone
know if such timers are still available? Or will I have no choice but
to change the three port valve with a three port mid-position type.

I realise that an upgrade to the mid-position type would give more
flexibility, but it's the wrong time of year to go ripping the CH system
apart now.

At present we are making do with a Switchmaster SM 805 timer. This
is slightly inconvenient as we have to allow the DHW to reach it's set
temperature before the CH is available.

Additional information;
Boiler is an Ideal ICOS 24 kw condensing heating only type in an
open vented system. Installed 18 months ago by a very decent
CORGI engineer.

Would be interested to hear from our resident experts

 

[chrishutt]

The simplest way of giving priority to CH over HW is to wire the HW call (from the programmer to the cylinder stat common) to the CH OFF terminal instead of the HW ON terminal. The hot water would then be heated whenever the CH was off, controlled by the cylinder stat.

 

[jackrussel]

The simplest way of giving priority to CH over HW is to wire the HW call (from the programmer to the cylinder stat common) to the CH OFF terminal instead of the HW ON terminal. The hot water would then be heated whenever the CH was off, controlled by the cylinder stat.

Thanks for the tip Chris, I'll go for that option.

Regards

Jack