Morning all, the time has come to replace my old Honeywell ST699 programmer. I understand that wiring changes will be needed but that the ST9400C is considered the "easiest" replacement. From what I've read, these are not without their own issues! Honeywell also do a THR860SWE TM2 programmer which, at first glance, looks pretty identical to the ST9400. Can anybody tell me what's the difference between the two and/or which one you'd recommend? Edit: I emailed Honeywell with this question 10 days ago and still haven't had a response, hence decided to ask here! Many thanks Spidey
Hi When considering what programmer to use, it’s the system it’s controlling that’s the issue. Can we assume you have a heat only boiler and a “y” plan system ? Do you want a programmable room stat, or hive type, ? and a photo of the existing programmer back plate wiring, is the way to get helpful reply , good luck Peter
It's an s-plan (two MV's, one for CH and one for HW) with heat from a heat-only oil fired condensing boiler. The ST9400 and TM2 controllers appear to both offer the same 2-channel 7-day setup (i.e. independent control of CH and HW) and on the face of it either is a suitable replacement. Neither will fit the existing backplate so will need rewiring, but the wiring differences between my old ST699 and the ST9400 are well documented and it is indeed a suitable replacement. I'm just trying to establish if there is any difference in real terms between the ST9400C and the "newer" THR860SWE (or TM2 as it's also referred). The basic bi-metal room stat I have is fine and I'm not interested in Hive or any other so-called "smart" technology, just these two specific programmers. Thanks Spidey