Lukewarm shower? Hot water that's suddenly weaker than it used to be on a unit you know is fine? It's often the tempering valve, a small mixing valve required by AS3500 on every hot water delivery to bathrooms in Victoria, with a 5-7 year service life. When they fail they fail unexpectedly, and the symptom is "all the hot water's gone". Prime Plumbing & Gasfitting replaces tempering valves across Melbourne, with the new valve set to the AS3500-required 50°C delivery temperature.
Quick answer: A tempering valve mixes hot and cold water to control the temperature delivered to bathroom outlets. A fault can cause lukewarm or excessively hot water even when the heater is working. Prime Plumbing & Gasfitting diagnoses the problem, checks the required valve and provides a written quote before replacement. BPC #103414.
Storage temperature and bathroom delivery temperature serve different purposes. The Building and Plumbing Commission explains that stored hot water needs protection against bacteria, while outlet temperatures are controlled to reduce scalding. The appropriate temperature-control arrangement depends on the water heater and the type of premises. A plumber checks the system and tests the outlets rather than assuming the whole hot water unit has failed.
A lukewarm shower does not necessarily mean the hot water unit needs replacing. A faulty tempering valve is one possible cause, so the valve and supply should be checked as part of the diagnosis. Replacing a faulty valve can cost less than replacing the whole hot water system. The price depends on access, the required valve and the work involved; the written quote confirms the cost before work begins.
Related plumbing topics:
AS3500 requires hot water delivery to bathrooms (basin, bath, shower) capped at 50°C. The tempering valve is set on install, we use a calibrated thermometer at the bathroom outlet during commissioning to confirm. Set too low and the shower is lukewarm; set too high and there's a scald risk. The right number is 50°C at the basin tap.
The replacement valve must suit the water heater, supply conditions and manufacturer instructions. Storage, continuous-flow and heat-pump systems can have different installation requirements. A heat pump is not a reason to lower the required storage-temperature protection. See the Building and Plumbing Commission hot water safety guide for the distinction between storage and outlet temperatures.
Tempering valve replacement is licensed plumbing work, BPC Compliance Certificate (#103414). The certificate is sometimes asked for at sale (particularly on healthcare or aged-care properties) and is part of the routine documentation we email after every Prime Plumbing & Gasfitting visit.
Before the valve, we check the unit's outlet temperature, sometimes the unit itself is the issue and not the valve. Five minutes at the unit confirms which is which.
Hot and cold isolations on the valve are closed, valve drained back to atmosphere, removed from the union connections. We document the make and model of the old valve in case there's a warranty claim possible.
New tempering valve is fitted with new union washers (we don't reuse old washers, they harden over the valve's service life and don't seal cleanly on a new install). Hot and cold isolations reopened.
The hot water draw is run at the closest bathroom basin while we adjust the valve. Calibrated thermometer at the basin outlet confirms 50°C. The valve's adjustment cap is then locked or sealed per AS3500 (so it can't drift).
Hot water at all bathroom outlets is tested in turn, basin, bath, shower, to confirm consistent delivery temperature. BPC Compliance Certificate emailed as a PDF along with the calibration record.
Most replacements run $280-$420 + GST supplied-and-installed. Variation is access (an under-floor valve takes longer than a wall-mounted one) and brand match (a unit-specific valve costs more than a generic). On-site quote in writing. *Pricing depends on lots of factors, every job is different. Budget for the higher side of the range; we'll quote the actual price on site.
If the kitchen tap runs hot but bathroom outlets are lukewarm, the tempering valve is one possible cause. The supply layout and other faults also need checking. A plumber can test the heater, valve and affected outlets before recommending a replacement.
Bathroom hot water needs suitable temperature control to reduce scalding. A tempering valve is one option; the correct arrangement depends on the heater, installation and type of premises. See the Building and Plumbing Commission hot water safety guidance and have a licensed plumber assess the existing system.
Service and replacement requirements vary by valve model and operating conditions. Follow the manufacturer's maintenance instructions. If outlet temperatures change or the valve cannot be set and tested correctly, arrange a plumbing inspection rather than relying on a fixed age estimate.
Use an appropriately licensed plumber for valve replacement. The valve must suit the system, and the outlet temperatures need to be checked after the work.
The required valve depends on the heat-pump model, supply conditions and the manufacturer's installation instructions. The plumber checks compatibility and the storage and outlet temperature controls when selecting a replacement.
The location must suit the installation requirements and allow access for testing and maintenance. If the existing valve is difficult to reach, discuss whether relocation is practical when the plumber assesses the job and prepares the quote.
Verified by Trustindex