Using the Theben TM 345 MF for a single-zone underfloor heating system
Overview
When Peter Arrow from Arrow & Son Ltd needed a cost-effective pump overrun solution for a small, single-zone underfloor heating (UFH) system, the usual approach did not make sense. Traditional wiring centres bundled with UFH manifolds were expensive, oversized, and offered far more functionality than required.
By switching to the Theben TM 345 MF delay timer, the installer delivered a cleaner, simpler, and significantly cheaper solution, without sacrificing comfort or control.
The Challenge
Most wiring centres on the market come with features that single-zone systems will never use. Their only real advantage for this scenario was the inclusion of a pump overrun, but the price point was disproportionate.
Peter wanted:
A cost-effective alternative to a full wiring centre
A reliable, adjustable pump overrun to protect the floor and improve comfort
A solution that was simple, compact, and easy to wire
No connection to boilers or other heating zones
They reached out to our UK team for support.
The Solution:
Theben TM 345 MF
After discussing the application with the installer, we recommended the TM 345 MF, a DIN-rail mounted multifunction timer capable of providing a fully adjustable delay-off function.
This approach allowed the installer to eliminate the wiring centre entirely, replacing it with a single, affordable Theben device
Application Details
Project type: 40 m² open-plan extension
Heating design: Single thermostat, one 2-port valve, dedicated UFH pump
Control goal: Maintain pump flow after heat call ends to average floor temperature and avoid hot/cold spots
How It Was Wired
TM 345 MF configuration (Delay-Off / RV Mode):
Permanent supply → A1 & A2
Live looped from A1 → terminal 15
Room stat call (zone valve brown) → B1 trigger
UFH pump live → terminal 18 (N/O output)
On-site adjustable overrun: Time (T) × Increment (Tx)
Operation:
When the thermostat becomes satisfied, the valve closes and B1 loses live. The TM 345 MF then holds its relay closed for the set delay period, running only the UFH pump. This averages the floor temperature and improves comfort across the zone.
Results
Peter achieved a clean, efficient, and highly affordable solution:
Total parts cost: £45–50
Savings: £80–200 versus any comparable wiring centre
Compact: Far less space required, cleaner installation
Independent: No interaction with boilers or other heating zones
Future-proof: Overrun time can be adjusted years later with a screwdriver
Comfort benefits: Customers clearly felt the difference in temperature consistency
The installer now plans to use this setup on every single-zone UFH job.
Why It Matters
This case is a great example of Theben’s installer-first approach:
simple, reliable, affordable control that solves real problems on site.
For electricians who want to streamline single-zone UFH jobs without compromising performance, the TM 345 MF offers a proven alternative to expensive wiring centres.