Horstmann 425TIARA Programmer, Black

Product Information

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. Hi all - no I haven't managed to remove it. Gave up after failing last time but it's more urgent now because the timer needs resetting almost daily now.

Although it says "not user serviceable" I thought I'd have a looksee anyway - I'm not without some skills in the repair and replacement of PCB components - however I can't get the bloody thing off the wall. 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.

Obviously this isn't ideal, you get a real mess if you try and use the timers, as each pin does something it isn't supposed to. Twin circuit hot water and central heating programmer. Offers 16 programmes for fully pumped systems incorporating motorised or mid-position valves and 10 programmes for gravity H.W./pumped heating systems.

As for your easy to understand explanation about my system, that was great, I'm a lot happier now I understand what is actually happening in my home. Will have another go when the need for heating diminishes in a month or so. Wife wouldn't be happy if I broke it at the moment. 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.This would not allow your system to work properly on the CH, so I have to assume you have already 'had a go'.