Central heating timer changing itself?

[Dan S. MacAbre]

Possibly a silly question, but hopefully not. Mum and Dad's CH timer occasionally (perhaps once every few weeks) changes from coming on twice (morning and evening) to once (i.e. all day). Mum and I are baffled, and although I've asked my dad if he's changing it, he denies all knowledge :-) Has anyone else had this happen? Maybe a button pressed against the contacts on the board (the change would require just one press of one button)? Or some kind of electrical interference?

[Davey]

What make and model of timer is it?

[Bob Minchin]

Internally is only has to miss the off pulse from the morning run to do what you describe and join up the two intervals. My programmer even has a facility to do this. turning on at the first session and off at the end of the last one for just one day before reverting to normal. Could be a failing power supply. SMPSU capacitors tend to give up the ghost after a few years as do the series capacitor volt dropping type power supplies.

[Dan S. MacAbre]

I'll check next time I visit. I was just wondering if it's the sort of thing that could happen to any of them.

[Dan S. MacAbre]

Well, I do have a capacitance meter - it'll be a good excuse to get it our of its box :-) I'll need to have a look inside to see if the case is fouling the buttons.

[Harry Bloomfield]

Dan S. MacAbre brought next idea :

A dodgy override button on ours (not that we have one) would do that. Does it have a program override button? It will put it on, if off, and remain on until the next programmed off period.

[Jeff Layman]

What is the default condition - eg after a power failure? If it is "on once" it could be suffering from an intermittent power loss and returning to its default state each time.

[Brian Gaff]

Many years back a neighbours electronic time was scrambled by a mystery problem. Turned out to be a fluorescent torch being used near to it. Just a thought, but normally when it is interference induced the results are random not always the same thing. Brian

[Cynic]

Mechanical or electronic?