The Totalhome TTH2CT is a twin-channel, 7-day full programmer designed for independent control of central heating and stored hot water. Manufactured by Resideo — the engineering team behind the Honeywell Home range — the TTH2CT is the direct replacement for the Honeywell ST9400C and is also compatible as a swap-out for the ST9400A, ST712A, ST722A, ST772, C21, C27, ST6300A, ST6200A, ST6400A, ST6450B, and THR860SWE. It fits the industry-standard backplate, so changeover requires no new wiring. With a large backlit text display, 3 on/off periods per day per channel, holiday mode, automatic summer/winter clock change, and a 3-year warranty, it is a reliable and cost-effective upgrade for any S-plan, Y-plan, or combination heating system.

2 Channel

Heating + Hot Water

7-Day

Independent Schedules

3 Periods

Per Day Per Channel

Holiday

Mode Included

3 Years

Warranty

⚠ Installer Notice
The TTH2CT operates at 230 V AC mains voltage and must be installed by a competent person. Isolate the circuit and prove dead before accessing the backplate or terminals. All wiring must comply with the current IET Wiring Regulations (BS 7671).

ⓘ What's in the Box
1 × TTH2CT 2-channel programmer | 1 × New industry-standard backplate | Installation and user guide

Key Features

Independent Dual-Channel Control

The TTH2CT gives completely independent scheduling for heating and hot water. This means the hot water can be programmed to come on earlier in the morning than the heating, or remain on longer in the evening — maximising energy efficiency and ensuring the system is never running either channel unnecessarily.

Large Backlit Text Display

Unlike older programmers with icon-only displays, the TTH2CT features a large backlit display with a line of plain text feedback. The screen clearly shows the current day, time, operating mode, and active channel status — making it simple for any household member to read and operate without guesswork.

3 On/Off Periods Per Day

Each channel supports up to 3 programmable on/off switching times per day, giving sufficient flexibility for most household routines — including morning, lunchtime, and evening heating or hot water periods. Programme indicator lights show at a glance which channels are currently active.

Holiday Mode

The dedicated Holiday button overrides the normal programme for a set period while you are away. Both channels switch off (or to a minimal setback) until the holiday period ends, at which point the programmer automatically resumes the regular schedule — no need to remember to reprogram on your return.

Auto Summer/Winter Time Change

The TTH2CT automatically adjusts for British Summer Time (BST) and Greenwich Mean Time (GMT) transitions — the clock moves forward or back by one hour at the correct moment without any manual intervention. The Extra Hour function allows a one-hour manual shift at any time if needed.

Industry-Standard Backplate — Easy Upgrade

The TTH2CT fits the standard Honeywell/industry-standard wiring centre backplate, meaning it can replace the ST9400C, ST9400A, ST712A, ST722A, C21, C27, ST6300A, ST6200A, ST6400A, ST6450B, and THR860SWE with no rewiring required. A new backplate is included for fresh installations.

Technical Specifications

Manufacturer Part Number	TTH2CT
Channels	2 (heating + hot water — fully independent)
Programming	7-day, up to 3 on/off periods per day per channel
Power Supply	230 V AC mains
Dimensions (H × W × D)	95 mm × 152 mm × 42 mm
Display	Large backlit display with text feedback
Override Functions	Temporary, permanent, Extra Hour, Holiday mode
Auto Clock Change	Yes — automatic BST/GMT (summer/winter)
Mounting	Industry-standard backplate (new backplate included)
Direct Replacement For	Honeywell ST9400C, ST9400A, ST712A, ST722A, ST772, C21, C27, ST6300A, ST6200A, ST6400A, ST6450B, THR860SWE
Warranty	3 years
Manufacturer	Resideo (TotalHome)

Frequently Asked Questions

What is the difference between a 1-channel and a 2-channel programmer?

A 1-channel programmer (such as the TTH1CT) controls only heating — hot water is either always on, always off, or follows the same schedule as the heating. A 2-channel programmer like the TTH2CT controls heating and hot water on completely independent timed schedules. This is essential for homes with a separate hot water cylinder (such as S-plan or Y-plan systems) where hot water demand does not mirror the heating schedule.

Will the TTH2CT fit my existing Honeywell ST9400C backplate?

Yes. The TTH2CT uses the same industry-standard backplate as the ST9400C and a wide range of other Honeywell programmers. In most cases the wiring can remain exactly as it is — just remove the old programmer from the backplate and clip the TTH2CT in place. A new backplate is included in the box if a fresh installation is needed.

How does the Holiday mode work?

Press the Holiday button and set the number of days you will be away. Both the heating and hot water channels are suppressed for the duration, saving energy while the property is empty. When the holiday period expires, the programmer automatically returns to the normal 7-day schedule — no need to reprogram or manually re-enable it on your return.

Can I give the hot water an extra hour without changing the whole programme?

Yes. The Extra Hour function extends the current active period for the relevant channel by one hour — without altering the underlying programme. It is ideal for moments when someone needs a shower outside the normal schedule or wants to extend the heating on a particularly cold evening. The programme resumes as normal after the extra hour.

Do I need to manually adjust the clock for daylight saving time?

No. The TTH2CT includes an automatic summer/winter clock change that advances the clock by one hour in spring and reverts in autumn in line with UK BST/GMT transitions. No manual adjustment is needed. The Extra Hour button is available if you ever need to apply a one-hour shift manually outside of the automatic change.

Thermostats – Smart Controls for Every Home