DIY Doctor

Main navigation

Honeywell ST9400C Programmer Switching Fault - Gives Hot Water or Central Heating not Both?

Postby dce52 » Mon Aug 03, 2015 7:46 pm

The programmer either gives hot water or central heating but not both. I can sometimes get both on it I tap the top right hand corner where the relays are. It also performs better if I turn off the backlight. The relays are energised with 48v but the unit only delivers 28v or 20v with both hot water and heating on and only 15v if the backlight it's on as well. Should I replace the relays with 24v ones (omrom g5la-1) or can I repair the on board power supply? It used to work when it was new about 4 years ago.
There are two 6mm dia 7mm high components on the PCB marked 961 22 63e with a black edge, are they the power supply?
Rank: Labourer
Progress to next rank:
Posts: 2
Joined: Mon Jul 13, 2015 2:31 pm


Simply Build It

Postby soundgeek » Tue May 16, 2017 8:21 am

Rank: Labourer
Progress to next rank:
Posts: 2
Joined: Tue May 16, 2017 8:14 am

Display posts from previous
Sort by
Order by

  • DIY How to Project Guides
  • DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!

  • Related Topics