Honeywell ST9400c Programmer issues - help please

[KksD]

It seems when the timer was re-fitted something has gone wrong. The symptoms are:


Heating only – works OK

Water only – works OK


However, when you want water and heating together.........the timer seems to go mad. Switching on/off multiple times.....clicking noises etc.

Can anyone advise what the problem might be?

 

[Echo the husky]

The unit is likely faulty and will need to be repaired/replaced, see here: https://www.diynot.com/diy/threads/need-to-replace-faulty-honeywell-st9400c.372984/