I have also found the following manual for it online and it also doesn't mention Option 40 so I was hoping there was an alternative fix maybe.

The TP5000 Si has a large, simple-to-read LCD display and can be easily installed with either mains or battery power.

The engineer scheme is here to support you and your clients, simply save yourself time and money on finding parts and gain access to our massive catalog of over 110,000 parts. The 103 third parties who use cookies on this service do so for their purposes of displaying and measuring personalized ads, generating audience insights, and developing and improving products.

Its programming capabilities and energy-saving features make it a practical choice for homeowners seeking flexibility and efficiency. Cookies are small text files placed on your device that remember your preferences and some details of your visit. Some cookies are essential to the functioning of this site whereas others are non-essential but help us provide a better browsing experience. The unit provides audible and visual warnings from 28 days before servicing is due and ultimately reduces the heating output should the due date pass. The wireless TP5000 Si is an easy to install-and-use 5/2 day programmable room thermostat which offers up to six time and temperature changes each day with different programmes for weekdays and weekends.Over time, even the most reliable thermostats may reach the end of their lifespan, requiring replacement. You can change your choices at any time by visiting Cookie preferences, as described in the Cookie notice.

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If you are unsure on the parts we have a technical team which can assist you at any time during the working day. Due to a built-in switching programme that the user may quickly modify to meet specific heating needs, it is simple to programme and operate.