Horstmann 425TIARA Programmer, Black

Product Information

If I pull hard, the box it's attached to in the wall starts to move too, and that's only fixed within a partition wall so it may not be as firmly implanted as need for the amount of force required. Personally I think they are fairly expensive for a mechanical basic clock, but they have been around for many years.

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. Its difficult to understand why this programmer has been used if your CH and HW is not already separate.Even if you had been able to access the back of the old one it doesn't look as if you would have been able to access the battery without 'serious leverage' anyway. Honeywell used to do programmers up to 4 or 5 zones, I think - now they seem to go with wireless room stats as you suggest.

What I really want to do is to install a NEST in place of the two thermostats, and a single timer for the water but I don't yet understand what wiring my system employs and how I might convert that for NEST. I am after a wiring diagram for it as would like to replace with a Horstmann H21XL two channel timer but am unable to find this particular model online.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. The Tiara is ideally suited for both gravity systems and fully pumped systems with either zone or mid-position valves. But it isn't a big deal to rewire a programmer, usually even the backplate wall screws are usually in the same places. I realised it as the boiler was still on one night when according to the programmer itshould have been off.

No more damage to anything although I did need to fill and strengthen the partitioning wall around where my previous attempts had ruined the structure. The 425 Tiara is a two circuit programmer for hot water and central heating and is ideal for use with gravity systems and fully pumped systems with mid-position or zone valves. It might be possible to introduce a motorised valve in the primary circuit (pipes going from the boiler to the HW cylinder). I can pull the main unit away from the stand-off enough to get a screwdriver into the gap but it's not coming away consistently - only where I exert pressure so much that the plastic deforms. 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.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. I am exactly at the same stage of trying to remove the same panel and only see it being stuck solid to the backplate. There's a baseplate which is fixed to the wall/hole in the wall onto which the controller should plug, and is secured with two screws on the top. There are lots of options, with a smallish number of variations, so if you decide what features you want we'll probably know of one which will do them.