Horstmann 425TIARA Programmer, Black

Product Information

I can get a screwdriver between the wall box and the stand-off but there's no way they are going to separate without my breaking one of them. Hey guys, it seems like you are all very helpful, and as I know very little about central heating/boiler systems (I still can't figure out whether I have a "Fully Pumped" or "Gravity Fed" system), I thought I would ask for help.

currentley have the Horstmann 425 Coronet single circuit timeswitch and the thing can lose an hour or more over a few days, so we are constantley messing with it. The list should not be considered a complete list of all available, excellent central heating controls. You can have things like one or two hour boost during an OFF period or addition to an ON time, 7 day control or 5+2 day, 2 or 3 on times per day, holiday timer, single button daylight saving adjustment. You should have a pump (Grundfos, Wilo) somewhere (in the boiler, if a system boiler) and either one 3-port motorized valve or two 2-port motorized valves. The heating controller's "life-long" battery must be dead (9 years old) because it regularly displays the incorrect time, leading to cold water at bath/shower time.The 31 and 37 3 channels use same backplate but different wiring, live is not available/linked L-2-5 as 2 and 5 are used for switching. i just would like to be able to programme at least 3 times aday and what exactly does using the existing backplate mean. And a pumped circulation for the energy to the radiators which is controlled by the pump being on or off.

Tiara, two channel programmer with 16/10 programme setting for fully pumped or gravity hot water/pumped CH systems. Anyway, I've been looking at the wiring diagram for the H27XL and comparing with the H37XL, and I'm trying to work out if I can use this 3-channel unit with my 2-channel system.I just like to have as much information with me prior to carrying out this changeover as I only want to do it once. Regardless, I've had my mains-shock already this month (replaced some light fittings in the hall and landing, and new light switches in the garage), so I'm back to being careful again. But it isn't a big deal to rewire a programmer, usually even the backplate wall screws are usually in the same places. I'd prefer not to break it as a replacement is some 90 quid, not to mention the loss of any hot water for the days it takes to turn up. Personally I think they are fairly expensive for a mechanical basic clock, but they have been around for many years.

Ideally I would still like to replace the timer as I would like different times for the weekends etc. You are right it’s not rocket science, I haven’t taken the cover of the old unit yet but I was a bit puzzled as to why I could not find a wiring circuit for this unit or any other correspondence for it online. If you are poking around with a screwdriver, make sure the system is isolated - there are live terminals near the top edge. I wonder if it's simply that the wiring box isn't firmly fixed, so is moving and not allowing the programmer to "snap" away from the backplate. Hi, I wish to replace the above timer with a 7day one that seperates the hot water and heating cycles.Handy for some circumstances, but as you say, room stats are really the way forward these days for lack of complexity and wiring. I realised it as the boiler was still on one night when according to the programmer itshould have been off.