HW controller problem (ST9100A)

[Epsom Pat]

Hi there,

My hot water has recently stopped being heated on its programmed schedule. After reading around a bit I decided it might be something to do with the water diverter valve, so I tried manually locking it open, resulting in the hot water being heated as long as the central heating is on and requesting water, but it doesn't come on as it's programmed to. One possible clue is that the hot water programmer, a Honeywell ST9100A, is behaving strangely - it flashes the screen and led light in sequence (see video). It looks like a deliberate error display, but I can't find any mention of it in the User Guide. This does not happen on programmed heating times, but does if I switch hot water on manually in any way on the programmer. The other controller on the right is for CH.

I have an unvented system similar to Megaflo, and I've tried changing the motor in the diverter valve in case it was getting stuck closed but that made no difference. I should mention that I *think* I'm looking at the correct diverter valve - I have three - for CH, HW, and ... towel rails maybe? I believe when we had the system put in we asked the plumber to set it up so that the towel rails would heat when *either* heating or hot water came on, so I've always assumed the third valve was some sort of logic device - it's right next to the hot water valve on the same pipe, and I don't think I've ever seen that valve close.

Any ideas? In case it's not obvious I'm no expert!

Thanks,
Pat.

 

[terryplumb]

Pat ,don't meddle with anything to do with an unvented system. Plumbers require a special qualification ( G3 ) to work on these systems and Diy'ers should steer clear. Regards Terry.