Horstmann 425 Tiara Programmer

With no digital screen and very few controls, the Horstmann 425 Tiara Programmer is as basic as they come. But just because it has that classic, old school timer appearance, it doesn’t mean its not up to the job. This is a simple to operate but very effective programmer. It’s as close to foolproof as you will find anywhere.



A lot of people buy this model to replace an older model Horstmann programmer, with reasons usually stemming from them not wanting or needing all the bells and whistles that the more advanced programmers have to offer . This model is a direct replacement for the older 425, and will also be a direct swap for other Horstmann models. Installation should be relatively trouble free.  

Quick Specification: 9 way standard backplate Diadem / Tiara 6Amp rated, Coronet 13 Amp. Troubleshooting: Want an explanation on how to operate the Horstmann 425 Tiara. Take a look at the simple video guide below.


The Horstmann 425 Tiara can control both the central heating and hot water. The intervals are 24 hours, all day, twice, and off. The mechanical timer dial (which operates in 30 minute increments) is capable of two “on” and two “off” commands per 24 hour period. Both the hot water and heating can be controlled individually. This model also has manual override. Overall an excellent no, nonsense programmer. But in reality, none are perfect.


Horstmann 425 Tiara Diadem Potential Problems / Faults

Whilst the Horstmann 425 Tiara (especially the earlier model) is a great programmer that should give many years of trouble-free service, there are a few reports of the clock stopping working. And also a few issues relating to the switches packing up.

However, the one area of concern that’s most troubling is the feedback from some reviewers stating that the newer model isn’t that reliable, and their particular unit stopped working after a short amount of time. Horstmann generally produce very reliable units so hopefully this is just a few faulty units that slipped through the net.

And if we look at any programmer, from any brand, whether that be Salus, Honeywell, Siemens, Danfoss or Horstmann, you will see that none of their products have a complete 100% positive, fault free related feedback from customers.

Where to buy. The most common outlet in the UK seems to be Screwfix. However, it is available in many other stores and online market places, including eBay UK, BES, BHL, Plumbnation and Amazon UK.

Related posts

Skimlinks Test