Tempering valve vs thermostatic mixing valve (TMV): what each does and which one you need

Tempering valve vs TMV: what each one does

A tempering valve and a thermostatic mixing valve (TMV) are both temperature control devices: they blend hot and cold water before it reaches the tap. The Australian Building Codes Board’s warm water handbook groups them together under that name.

A TMV is built to hold a preselected temperature that’s safe for direct contact with skin, and to shut down if the cold water supply is lost. TMVs are commonly used in hospitals, schools and aged care facilities, with a requirement for annual testing.

New and replacement home systems in Queensland need a temperature control device, such as a tempering valve. Adjusting or replacing either valve is a job for a licensed plumber in Queensland.

What a tempering valve does on a home hot water system

A tempering valve lets your hot water system store water hot enough to control bacteria, while sending cooler water to the bathroom. The Queensland Government says residential hot water storage must be heated to at least 60°C to prevent bacteria such as Legionella, and that a temperature control device must deliver hot water to taps at a maximum of 50°C.

The ABCB handbook defines a tempering valve as a temperature-actuated mixing valve that tempers heated water with cold water to give a lower temperature. One maker, Caleffi, describes its tempering valve’s thermostatic element as fully immersed in the mixed water.

The kitchen and laundry don’t always go through the tempering valve. The ABCB handbook notes that untempered branches can serve fixtures not used for personal hygiene, such as kitchen and laundry sinks, so hotter water at the kitchen tap isn’t automatically a fault.

A temperature control device must be fitted to all new and replacement hot water systems in Queensland, so if your system is being replaced, a temperature control device comes with the job. Our choosing a hot water system guide covers the rest of that decision.

What a thermostatic mixing valve (TMV) does, and where it is required

A thermostatic mixing valve controls the mixed water to a preselected temperature using a thermostatic element or sensor. The ABCB handbook says a TMV usually contains non-return valves, line strainers and isolation on both the hot and cold inlets. Those parts let a plumber test the valve’s thermal shutdown: if the cold supply is lost but hot water is still available, the TMV shuts off until cold water returns.

TMVs matter most where people can’t react quickly. The handbook notes that scald risk is far greater for people with disability, the elderly, children and infants, who may have slower reactions and thinner skin. Water for personal hygiene is generally limited to 50°C, and to a maximum of 45°C in certain high scald-risk situations.

TMVs are not fit and forget. The handbook says that in Queensland, TMV maintenance must be done by an appropriately licensed plumber, and that AS 4032.3 (2004 edition) sets field testing at intervals of no more than 12 months unless a risk assessment sets another interval.

Tempering valve vs TMV side by side

The table compares the factors that matter. Neither valve is better in every home: the right one depends on who uses the water and where.

Which valve does your home or property need?

The valve a property needs depends on who uses the hot water and whether the hot water system is new, replaced or existing. Use this as a guide to the conversation with your plumber, not a compliance ruling.

Landlords and property managers looking after care or commercial sites can book testing through our TMV and backflow service.

Signs a tempering valve or TMV is faulty

A faulty tempering valve or TMV usually shows up as water that’s too cool, too hot, or changing temperature mid-shower. Rheem notes that hot water that isn’t hot enough could be a faulty tempering valve over-cooling the water, and that a plumber can test the system and replace the valve if needed. Caleffi’s fault-finding table lists fluctuating temperature, erratic or no flow, and hot water at the cold taps.

Safe checks you can do: look for drips at the valve and system, note which taps are affected and when, photograph the valve and the system’s label, and if the water is scalding, stop using the hot tap and call a licensed plumber. If the valve or system is leaking, read our leaking hot water system guide.

Adjusting or replacing these valves is licensed work in Queensland

Adjusting, servicing or replacing a tempering valve or TMV is work for a licensed plumber, not a weekend job. The QBCC says most plumbing work in Queensland is regulated and needs a QBCC licensed plumber. The short list of unregulated work owners may do covers jobs like replacing a shower head, a filter cartridge or a tap washer.

Even the lightest regulated category, minor work, must be done by a QBCC licensee, and the QBCC lists maintaining, repairing or replacing a fitting in that category. Caleffi’s manual says tempering valves must only be installed by a licensed plumber, and the ABCB handbook says TMV maintenance in Queensland needs an appropriately licensed plumber.

The hot water system’s thermostat is off limits too. The Queensland Government advises not to turn down hot water systems, and says any thermostat adjustment should be done by a licensed electrician.

What a plumber checks, and what affects the job

A plumber checks how the valve performs against the standard and the maker’s instructions, then decides whether a service or a new valve is the safer fix. AS 4032.3 sets the requirements for field testing, maintenance and replacement of TMVs, tempering valves and end-of-line devices. Caleffi, for example, recommends checking its tempering valve at least every 12 months, cleaning the inlet strainers and checking the check valves seat correctly, and replacing the valve after 5 years of service as a safety measure.

No two jobs are the same size. What affects the work:

• Valve type: a tempering valve or a TMV, and whether the existing model can be serviced.
• Access: how easy the valve is to reach on the system or in the wall.
• Condition of the hot water system and the pipework around the valve.
• Whether the system itself needs work, such as a fault behind the temperature problem.

Getting a tempering valve or TMV checked

Getting a tempering valve or TMV checked starts with a call to a licensed plumber. Jim Monger Plumbing and Gas fits tempering, relief, isolation and pressure limiting valves, and provides thermostatic mixing valve installation, testing and yearly maintenance for commercial and care facilities.

We work from Victoria Point across the Redlands, Logan and Brisbane under QBCC licence 15504687 and gas licence L90908. For homes, start with our Victoria Point hot water service. For care and commercial sites, see TMV testing and backflow. Call 0418 871 269.