Central heating faults

[someonelse]

I have 2 faults: (1) intermittent long-standing I can live with and (2) new, needs fixing

Set up is

• conventional oil boiler with attic tank and airing cupboard cylinder (backed up with immersion)
  
  
• Honeywell ST 6400C heating and water programmer. Hot water permanently off, with 1 hour over-ride used when needed. Central heating permanently on and controlled by....
  
  
• Drayton Digistat RF2 which calls for heating when temp drops below set levels at set times.

1. When pressing 1 hour over-ride, the entire heating system electrics (and boiler) sometimes switches off (1 in 10 times?), then on again after 3-4 seconds. Over-ride then works when re-pressed.
   
   
2. Boiler has suddenly started firing up and then off, for no good reason. Neither hot water nor heating being called for, but the Digistat receiver in airing cupboard shows green light (usually comes on when transmitter calls for heat), and 'buzzes' (usually silent).

I'm assuming boiler is fine (recently serviced) but Digistat faulty (15 years old?). Replacement Digistat is the +2RF.

Q1 – if I buy replacement Digistat, how easy is it to wire? For context, I'm not an electrician but am reasonable at DIY. Replaced/wired-in new 3 port valve myself last year by connecting wires 'like-for like'.

Q2- Would it make sense, given the long-standing Honeywell fault to either

1. open Honeywell to check for loose wire, and/or
   
   
2. replace the Honeywell (with ST9400C) – (easy or complex to wire in?) as well as the Digistat, or
   
   
3. re-design controls and replace with a single, simple radio programmer, and if so what?
   
   Cheers!