Thermostatic mixing unit Termojet for underfloor heating manifold TJ-MU-10B

The pump-mixing unit Termojet TJ-MU-10B is a compact, ready-to-install solution for connecting an underfloor heating circuit to a boiler or heat pump. The built-in thermostatic three-way valve of the TMV series automatically maintains the supply temperature in the range of 20–43°C without any electrical power. The unit ensures circulation of the heat-transfer fluid through the floor loops and protects the screed from overheating — completely passively, without controllers or sensors.

Technical Specifications

Operating Principle: TMV Valve

The heart of the unit is the thermostatic three-way mixing valve TMV with a built-in thermosensitive element. It continuously monitors the outlet temperature of the heat-transfer fluid and automatically blends cooled return flow with the hot supply from the boiler — until the underfloor heating circuit temperature reaches the set limit in the range of 20–43°C.

The process is entirely passive: no electrical power, no external sensors or capillary tubes. The thermosensitive element expands or contracts directly inside the valve body — mechanically moving the spool, changing the ratio of hot and return flows. Learn more about TMV thermostatic valves in the Termojet valve catalogue.

Application Scenarios

• Boiler + underfloor heating. The boiler delivers 70–80°C — the floor needs 30–40°C. The TJ-MU-10B unit solves this automatically: the TMV valve blends in the return flow and reduces the temperature to a safe level. An essential component when connecting an underfloor circuit to a high-temperature boiler.
• Compact installation. The TJ-MU-10B is designed for smaller systems — an apartment, a small house, a few rooms. The compact dimensions simplify installation in a manifold cabinet or technical compartment.
• Zone heating. In combination with the 6-outlet manifold with flow meters, the unit provides a separate temperature regime for the underfloor circuit within the overall house heating system.
• Renovation. Replaces an outdated or missing mixing solution without re-routing pipes — installed inline in the existing supply.

Advantages of the TJ-MU-10B Unit

• No electrical power. The TMV valve operates solely on the thermal energy of the heat-transfer fluid — no dependence on the electrical grid, no wiring to the unit required.
• Ready assembly. The pump and valve are assembled into a single compact unit — minimum installation connections, minimum time expenditure.
• Screed protection. The TMV valve will not allow heat-transfer fluid hotter than 43°C into the underfloor circuit — the screed, PE-RT pipes and floor covering are protected from overheating regardless of the boiler temperature.
• Easy maintenance. The absence of electronic components reduces the probability of failure and simplifies diagnostics.

Underfloor Heating and Heat Pump

A heat pump generates heat-transfer fluid at 30–50°C — exactly the range at which underfloor heating operates most efficiently. With a low-temperature source, the TMV valve of the TJ-MU-10B unit does not restrict flow: if the supply temperature is already within 20–43°C, the valve is fully open and creates no additional hydraulic resistance. The unit remains useful for hydraulic separation of circuits even when a heat pump is the primary heat source. For comprehensive underfloor heating schemes powered by a heat pump, visit the Termojet heat pumps website.

Frequently Asked Questions

Is a mixing unit needed with a heat pump?
If the heat pump is already configured for a low supply temperature (35–45°C) and there is no need for hydraulic circuit isolation — the unit may not be mandatory. However, in a bivalent scheme (heat pump + boiler) or when multiple circuits with different temperatures are present, a unit with a TMV valve simplifies hydraulics and eliminates the risk of floor overheating from the boiler during transition modes.

What is the difference between TJ-MU-10B and TJ-MU-40A?
TJ-MU-10B is a compact unit for smaller systems, TMV valve temperature range: 20–43°C. TJ-MU-40A is a more powerful variant with an extended range of 25–55°C, aimed at larger installations with higher capacity. The choice depends on the area of the underfloor circuit and the required thermal load.