Thermal Relief Valves

Let go of the trigger and your pump keeps pumping, recirculating the same cup of water until it gets hot enough to melt packings. The thermal relief valve is the cheap little part that dumps that hot water before it wrecks a pump worth hundreds. Sun Brite Supply carries General Pump and Suttner thermal relief valves from 140 to 190 degrees in 1/4, 3/8, and 1/2 inch threads. Not sure which your pump takes? Call 301-519-9274.

How a Thermal Relief Valve Saves Your Pump

When you release the trigger, the unloader sends flow into a bypass loop instead of out the nozzle. The same water then laps the pump head over and over, picking up heat every pass. In a few minutes of bypass on a hot day, that trapped water can pass 140 degrees, and packings and o-rings start dying fast above that. The thermal relief valve sits in the pump head or bypass line with a temperature element inside. At its rated temperature it pops open, squirts the overheated water on the ground, pulls fresh cool water in behind it, and reseats. The puddle under your machine after idling is not a malfunction. It is the valve doing its job.

145 Degree or 190 Degree: Which Rating Do You Need?

Cold water machines fed by a garden hose want the standard 140 or 145 degree valve. That rating trips well before bypass heat reaches packing-killing territory. The 190 degree valves belong on machines that see hot incoming water, like hot water skids or rigs drawing from heated tanks, where a 145 valve would dump constantly even though nothing is wrong. Match the thread to the port on your pump head, 1/4, 3/8, or 1/2 inch MPT, and match the temperature to your water source. Putting a 190 valve on a cold water machine to stop nuisance dripping just removes the protection earlier heat should have triggered. Fix the real cause instead, which is usually too much time in bypass.

Thermal Relief Valve Lookup

Call first for current availability and we will set one aside.

From the Field

We rebuild a lot of pumps that died in a parking lot while somebody answered a phone call with the trigger off and the engine running. The autopsy is always the same, melted packings and scorched o-rings, and half the time the thermal relief valve had been removed and replaced with a plug because it kept dripping. That drip was the warning. A ten dollar valve was trying to prevent a several hundred dollar rebuild. Our counter rule: replace the valve any time you rebuild a pump, test it each season by letting the machine idle in bypass for a few minutes and confirming it discharges, and if long bypass time is part of how you work, shut the machine off between surfaces instead of letting it cook.

Related Collections

• Pressure relief valves
• Safety relief valves
• Unloader valves
• Easy start valves
• Check valves
• Rupture discs
• Thermostats
• Pressure washer pumps
• Pump accessories

Stop by the Gaithersburg counter and we will match the valve to your pump on the spot.

Frequently Asked Questions

What does a thermal relief valve do on a pressure washer?

It protects the pump from bypass heat. With the trigger closed, water recirculates through the pump and heats up fast. At the valve's rated temperature it opens, dumps the hot water, draws in cool water, and closes again.

Why is water squirting out of the bottom of my pressure washer?

If it happens after the machine idles with the trigger off, that is the thermal relief valve discharging hot water on purpose. If it drips constantly from cold startup, the valve has failed and needs replacement.

At what temperature does a thermal relief valve open?

Most cold water machines use valves rated 140 to 145 degrees F. Valves rated 190 degrees F are for machines fed with hot water, where a lower rating would discharge constantly.

How do I test a thermal relief valve?

Run the machine and leave the trigger closed for three to five minutes. A working valve will discharge water from the pump area, then reseat. No discharge while the pump head gets too hot to touch means the valve is stuck and due for replacement.

Can I just plug the port instead of replacing the valve?

No. A plugged port removes the only heat protection the pump has, and a long phone call in bypass can cook the packings in minutes. The valve costs about the same as a repair kit o-ring set and a whole lot less than a pump.

Which thermal relief valve fits my pump?

Check the thread size on the port, usually 1/4, 3/8, or 1/2 inch MPT, then match the temperature rating to your water supply. Send us your pump model at 301-519-9274 and we will confirm the fit before you buy.