Best Replacement Central Heating Programmers

by Editor on November 6, 2016

How to find the best replacement central heating programmer for your system

Replacing your central heating controls can be a good way of upgrading and making your system more efficient. Changing the heating programmer should be simple if you swap to a model recommended as a “direct plug-in replacement”, but not all controls use the same back plate and the wiring connections may need to be changed over.


Potterton EP2002 Backplate

Heating controls from manufacturers such as Randall Horstman, Drayton, Honeywell, Potterton and Siemens are updated on a regular basis and issued with new model numbers. These updates are often superficial and the actual unit won’t have changed very much, but it’s essential to find out if the new replacement programmer is compatible with your system.
You’ll find a list of the best replacement programmers below.


Search for Central Heating Programmers

There may be subtle differences in updated and new version of your central heating controls. Some models with different part numbers will look almost identical, so finding a replacement programmer will be easier if you look for the same manufacturer as your existing unit.

Choosing a replacement programmer for your heating system will depend on several factors:

Number of Program Channels

The number of channels needed is important. For a combi boiler system where the boiler supplies hot water on demand you’ll only need a single channel programmer for the heating. If your timer controls both the hot water and heating you’ll need a 2-channel timer, and if your slider or switches are interlocked so you can only select HW or HW and CH, but not CH on its own (as with a gravity hot water system) you’ll require a programmer with a similar interlock. Most 2 channel programmers will give you this option  by setting a switch or link on the back of the unit.

Central heating programmers normally have 1, 2 or 3 channel options to suit the different system requirements:

  1. Central Heating Only- as with a combination boiler where the hot water is supplied from the boiler on demand (not stored in a tank).
  2. Hot Water and Heating- as used with system boilers.
  3. HW, CH and an additional heating zone- as used where underfloor heating requires separate time control.

Ease of use

Analogue clockwork timers were originally considered to be the most reliable and simplest heating programmers to use. Many mechanical rotary clock type central heating timers include added features such as battery backup, but most heating engineers and end users now prefer digital programmers because they provide more accurate timing and also boost options. The majority of end users are now familiar with the operation of electronic timers and modern digital programmers are designed to be user friendly.

Programmer Replacement- Same Plug-in Base

The easiest option is to replace a central heating programmer with the same model as your existing one. Changing for a direct plug-in replacement which fits exactly the same sized wall plate is usually a matter of turning off the heating system at the main switch and doing a straight swap with no wiring involved.

Please Note- It’s important that your system has an isolation switch and the correct fuse for safety. The main heating switch should turn off (isolate) the whole heating system including the boiler, and have a maximum 3 Amp fuse fitted. If you’re not sure of how to completely turn off the electrical power your system then you should call your heating engineer or an electrician.

Standard Back-Plate

Many early central heating systems used a clockwork rotary timer such as a Honeywell, Landis and Gyr, Potterton Mini-Minder or SwitchMaster 400 which all had a 6 pin industry standard back-plate. This was often called the British Gas Standard Backplate and is still used for many modern digital programmers.

Programmers using the standard backplate can be removed by loosening the programmer’s two retaining screws (not removingthem!), hinging the unit upward and it lifting off.

The standard 6 terminal backplate wiring from left to right is:

  • N-  Neutral
  • L-  Live Feed
  • 1-  HW OFF (Y Plan & Flow Share systems)
  • 2-  CH OFF (Not normally used)
  • 3-  HW ON
  • 4-  CH ON

Sometimes there is no terminal for the earth wires which will need to be connected together in an insulated 5 Amp connector block.

Manufacturers such as Drayton, Myson, Honeywell and Siemens regularly issue new programmer models that do fit onto the standard base. Check the latest model number and physical size against yours to be sure that it will be a direct replacement for your programmer. See the list of programmers below for backplate info.

As a professional electrician I’m always keen to replace the old base even if it’s quicker to do a straight swap. The connections on old back plates can become worn with age and poor electrical connection can cause faults. For your own installation the condition of the back plate really needs to be assessed and replaced accordingly.

Programmer Replacement- Different Base

Some models will state they they are a “direct replacement without any rewiring” but this only applies if you swap for the same model or baseplate type.

If you’re upgrading from a very old model or a mechanical rotary timer to a digital central heating programmer and you can’t find a direct replacement with exactly the same base then things can become slightly more complicated. The connection wall plate or baseplate will require changing which involves disconnecting the wiring, refixing the baseplate (new screw holes) and then reconnecting as per the same or new wiring configuration.

Some earlier exceptions to the Standard Base were the Danfoss Randall 3020, Randall 3060 and Randall 4033 which were very large mechanical clock units. The Randall 102, 103 and 1020 GP Range of programmers also had rotary dials which were very easy to use but had a different wall plates from any other models. Replacement units are still available for the Randall 3060, 4030 and the 103 although some don’t come with a new wall plate.

Horstman and Potterton programmers have their own different versions of backplate. It’s also worth noting that the Honeywell ST699 and ST799 don’t fit a standard backplate and are released by pushing up a tab at the bottom of the unit with a screwdriver.

It’s important to completely turn off your heating system and boiler (as described above) before disconnecting anything. If you’re going to attempt any wiring yourself then be sure to make a note of the connections and take a photo before you start. If you’re unsure of this then it’s best to get help from a qualified electrician.


Here are some of the best models for Central Heating Programmer replacements:

Single Channel Programmers

Horstman 425 Coronet


Horstman 425 Coronet Timer

The Horstman 425 Coronet is single channel mechanical rotary timer suitable for central heating control switching on and off twice every 24 hours. The Horstman 425 Tiara and Diadem Electro-mechanical Programmers are the 2 channel versions. Earlier models had an indicator light but this seems to be missing from later models.

Salus EP101- Glow Worm


Salus EP101

The Salus EP101 Glow Worm single channel central heating timer with a large blue backlight display. As used by Glow Worm heating systems. Programmable for 7 days with 3 on and 3 off switching. Wiring option for volt free boiler contacts.

Danfoss Randall TS715


Danfoss Randall TS715

The Danfoss Randall TS715 single channel electronic timer provides voltage free output contacts making it an ideal solution for use with both mains voltage and low voltage control circuits. Can be configured for 7 day, 24 hour, or 5 day/2 day operation and either 2 ON/OFF or 3 ON/OFF per day. It has a permanent backlit display. Can direct replace any other 1 channel programmer using the British Gas Standard Wallplate.

Randall 103 Rotary Timer


Danfoss Randall 103

The Danfoss Randall 103 is a basic 1 channel Timeswitch. It has 24 hour- 2 on/off and advance. This is a direct plug-in replacement for the 103 and is not compatible with any other programmer back plates.

Danfoss Randall 103E (Electronic)


Randall 103E

Danfoss 103E7 Electronic Single Channel with 3 on/off. Ideal for upgrading an old 103 mechanical clock to a more accurate electronic version. Clearly shows state of output. 5/2 day or 7 day operation and incorporates extra programs and overrides. The model clearly shows the current state of the output. 


2 Channel Central Heating Programmers

Randall 3060


Randall 3060

The Danfoss Randall 3060 2 channel programmer. Large wall plate will fit as replacement for existing 3060. Easy to operate with large dial and timer tabs for control of gravity hot water and pumped central heating. 24 hour rotary clock. 2 on and off events per day. Not compatible with any other back plates.

Randall 4033


Randall 4033

The Danfoss Randall 4033 Central Heating Programmer. Large wall plate will fit as replacement for existing 4033. Easy to operate with large dial and timer tabs. Runs Heating and Hot Water independently for fully pumped heating systems. Provides 2 ON Times & 2 OFF Times Per Day. Not compatible with any other back plates.

Drayton LP522 Lifestyle *Recommended- Good Value for money*


Drayton LP522 Lifestyle

The Drayton LP522 Lifestyle range 2 channel 5 day/2 day programmer (separate timings for heating & hot water). Has large buttons and uncomplicated controls fits standard base. 3 timing periods per day with weekday and weekend options. Memory saver – program and clock never need resetting in the event of loss of power. Easy to read, backlit screen. Automatic summer/winter time change. Boost button gives 1, 2 or 3 hours with LCD indication. Will be direct plug-in replacement for any standard backplate programmer.

Honeywell ST9400


Honeywell ST9400

The Honeywell ST9400 has large backlight display. Factory set Clock. Automatic Summer/Winter time change. 7 Day or 5/2 Day operation. Fits standard base. Direct plug-in replacement for Honeywell ST6400 programmers without the need for re-wiring.

Danfoss Randall FP715


Danfoss-Randall FP715

The Danfoss-Randall FP715– 2 channel central heating control has a 7 day, 5/2 day or 24 hour programming function. Permanent back lit display. AM/PM or 24 hour display. Ready to go built-in programmes. Timer options either 2 ON/OFF’s or 3 ON/OFF’s per day. Can direct replace any other 2 channel programmer using a Standard Wallplate.

Siemens RWB29


Siemens RWB29

The Siemens RWB29 is a 2 channel programmer that has daily, 5/2 day or 7 day programming. Two or three on/off’s per day and independent timing for hot water and central heating. Recommended as a direct replacement for MicroGyr and the RWB9 range. Fits a standard back-plate.

Horstman C21


Horstman C21

The Horstman C21 electronic heating programmer. 3 on and off settings for HW and 3 on and off settings for CH per day. One hour boost HW (only) and instant advance for CH (only). 18 months battery back up. Direct replacement for the Honeywell C21 and Newlec NLC21. Non standard backplate.

Danfoss Randall FP975


Danfoss FP975

The Randall FP975 2 channel programmer offers 3 On and Off settings per day. AM/PM or 24 hour display. Advance / override. A direct plug-in replacement to the Danfoss Randall MK9 range (types 922 & 972), the Danfoss Randall SET5, or any other programmer using the British Gas standard wallplate.

Potterton EP2-2000


Potterton EP2

The Potterton EP2 is a 2 channel programmer has advance over-ride function, 24hour, 5/2 day or 7 with 2 on and 2 off timed settings. The base is larger than standard but can be a direct plug-in replacement for the P2000, EP2001, EP2002, EP3002 and EP6002.


3 Channel Central Heating Programmers

3 Channel Programmers are ideal for hot water and central heating radiator systems with an extra zone which is often used for Underfloor Heating. The benefit of having a 3 channel timer is that all the controls are in a central location rather than spread around in different rooms as is usual with a heating installation using programmable room thermostats.


Horstman H37


Horstman H37 ChannelPlus

The Horstman H37 ChannelPlus is a 3 channel programmer giving independent timing of each channel on a 7 day programme. Ideal for the control of two heating zones as well as hot water. For use with fully pumped systems. 3 channel – 7 day electronic programmer. Independent settings for 3 separate zones with 3 on / off periods. Pre-set clock. Auto winter / summer time change. Non standard wall plate.

Reliance 3 Channel Programmer *Recommended- Good Value for money*


Reliance 3 Channel Controller

The Reliance 3 Channel Programmer has Large Easy to Read Clear Illuminated Screen Display. Programming for Gravity or Pumped Hot Water, with a Choice of 2 or 3 Programmes per Day. 7 Day, 5/2 Day or 24 Hour Programming with Boost and Advanced Feature on All Channels. It is perfect for Fully Pumped Central Heating Systems with 3 Separate Heating Zones. 2 year Guarantee. Standard back plate.

{ 14 comments… read them below or add one }

Raj November 24, 2018 at 17:26

Hi, if I put a Hortsmann channelplus XL27 programmer onto a back plate of wired Honeywell ST9400C programmer, will it work? Thanks, Raj.

Hi Raj
Probably best to change the backplate if the wiring looks different.
There’s a good compatibility guide here –
Best regards

Phil Adwick November 8, 2018 at 07:18

I am on my third Honeywell ST9400c. What other units fit the same backplate please. Lost confidence in Honeywell

Hello Phil
The Drayton LP522 is a reliable programmer and I’m fairly sure it fits the Honeywell backplate.
All the best

Graham November 4, 2018 at 10:11

Just woke up this morning and no heating. My Grasslin QE 2 has gone south!!
Please can you reccommend a replacement, programmer. I can get hold of a Grasslin QEG 2 which uses the same backplate, which would be handy.
What do you think?
Any help greatly appreciated.

Hi Graham
The Drayton LP522 would be a good option. However you may need to change the backing plate. There’s a good compatibility guide here-
All the best

Ben June 6, 2018 at 22:02

Perfect thanks Steve

Ben June 6, 2018 at 19:11


I have just purchased the Honeywell st9400. Am I right in saying that the boiler supply is fed from a 3 core 3amp fused spur and the Honeywell controller then takes a live and neutral feed from the boiler along with 2 switched lives for CH ON and DHW ON ? So in essence this this requires a 4 core cable from boiler to Honeywell programmer? (No earth in programmer required?)
Thanks in advance for any info

Hi Ben
Yes that sounds right but the cable to the programmer should have an Earth even though it’s non metallic. All electrical accessories and cables should have an Earth conductor.
All the best

John Advent April 24, 2018 at 14:10

I’m looking at replacing a central heating programmer. I didn’t realize how many different ones were on the market. This has helped me lots, especially the difference in back plates. Thanks very much for the info.

Crispin Andrews April 13, 2018 at 13:20

I wonder if you would know the answer to this. My Aunt has a very old (dated 1999) Danfloss 3060 programmer with a knob to select programes. Would the Danfloss 4033 Switch type Programmer be a straight swop on the old 3060 backplate requiring no change to wiring? She finds the knob hard to twist around due to arthritus. The click switches would be easier.

Hi Crispin
The back plates to 3060 (gravity) and 4033 (fully pumped) are not interchangeable.

Melissa Robotham April 11, 2018 at 08:52

I have just had a new oil fired central heating system fitted and need a 4 channel programmer.
Im look at the Hortsmann Channelplus H47XL or the Drayton Mistime Channel T742R. Which one would be better out of the two? quality, functions etc? or if anyone can recommend an alternative choice that would be great. Thanks in advance.

Jay March 20, 2018 at 16:18


I’ve just had my gravity fed central heating timer switchmaster 600 failing to operate and requires replacement. What would you recommend for a digital replacement timer I’m considering RWB29 from Siemens’s or Drayton 25473 LP112- 2 channel programmer, which would you recommend that would fit my existing back plate with 6 terminals?

Looking forward to your earliest response.

Many thanks
Hi Jay
The DraytonLP would be a good choice
All the best

Mazhar Saied March 20, 2018 at 08:43

Hi, I am looking for a replacement of British Gas Emp2 programmer(approx 20 years old). Can you please suggest compatible programmers (with exactly the same base plate) for 7 days separate settings for HW and CH. Thanks.
Hi Mazhar
The 2 channel Drayton LP would be a good replacement.
All the best

Alastair Nesbitt January 11, 2018 at 22:07


I am having problems with my programmer which is a Randall 103E.

Will the Danfoss Randall 103E7 be a suitable replacement?


I reckon the 103E7 would be a good replacement Al.

Tom January 2, 2018 at 13:43


What would you recommend to replace an old switchmaster 400 and will it involve changing the baseplate?

Any 2 channel org should do. More info
All the best

Brian November 13, 2017 at 11:44

I have 4 wires going into an old Landis & gyr rwb200 can I replace it with a Drayton lp722 MK4 without rewiring the old system did no let me have hot water on by itself.

Yes. The 722 gives you separate control of HW and CH.

Keith Thompson August 10, 2017 at 15:49


I am looking to replace an old analogue / clock programmer.
It is a Towerchron Model FP.
I have photo but your site will not let me paste into this message

Can you suggest compatible dual channel programmer?

Thank you in anticipation
Hi Keith. The Drayton 522 is a popular 2 channel programmer.

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