Heating control problem

[ROBINSE]

Hello,

Please can help. I have the following heating system:

Potterton Prima 30e boiler

Honeywell room thermostat

Honeywell ST6400C Heating / Hot water control, and timer.

It works fine if I have just the hot water, or the heating switched on. However, when I switched switched the central heating on today in addition to the hot water - which was already on, the heating control switches itself off.

I have tried each independently, and they both work fine, and I have also adjusted the thermostat, and that appears to be working.

Could it be the motorised valve that needs replacing, if so would you recommend I stick to Honeywell parts, or do you know of an alternative brand just as good. Thanking you for your assistance.

 

[bengasman]

The whole idea of having completely independent timing, like with the 6400, is to avoid using ch and dhw simultaneously. A proper cylinder heats up in less than half an hour, and stays hot for more than 12 hours.
If you must have it on at the same time, my first guess would be a faulty diverter.
Are you absolutely sure that ch and dhw came on together before? Any work done at all?

 

[Rox]

There are different controls plans, most often S Plan and Y Plan. See 'System Plans' on the downloads tab at www.honeywelluk.com
Perhaps info there will help.
I recommend you use Honeywell products - maybe they cost a bit more but you're paying for their reliability and quality, that's why most installers use them.

 

[kevplumb]

sure its not on a "w" plan