Guide to Mixing Valves & Anti Scald Valves on Water Heating Equipment
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• Mixing valves - anti-scald valves on heating boilers, tankless coils, & water heaters
• Troubleshooting heating system boiler controls and switches
• What are the basic components of heating systems?

This website answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs. The photo above shows a modern cad cell relay on an oil fired heating boiler - one of the safety controls which we discuss in this article. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

Guide to Mixing Valves and Anti Scald Valves on Heating Equipment

When a heating boiler uses a tankless coil to produce domestic hot water, a third single-function control may be installed for that purpose. In this photo a Honeywell limit control switch is being used to monitor hot water temperature at the tankless coil which is in turn mounted on a steam boiler of an older home in Portland, Maine. You can see the black-handled mixing valve in the lower right of this photo.

Cold water from the building is entering the tankless coil via the bottom pipe (green corrosion) and hot water, heated by the coil is leaving at the upper part of the tankless coil, where it turns downwardfs to enter the left side of the mixing valve.

Additional cold water is permitted to enter the bottom of the mixing valve, and tempered (non-scalding) hot water then leaves at the right side of the mixing valve in this photo.

In this picture of a more traditional single-function heating boiler limit control, the limit switch is being used on a tankless coil, and in the enlarged version of the photo you'll see that the temperature limit on the control is set to about 140 degF.

Anti-scald valve used with water heater limit switch: In this photograph, which we also show at page top, a single function limit switch is in use on a water heater, not on a heating boiler.

Here too you will notice that there is also a mixing valve installed to prevent scalding - the gray-handled device to the right of the control (and leaking we might add).

The use of a mixing valve or anti-scald valve permits us to set the Honeywell 6006 limit control switch to a higher number, keeping the water in the heater at a higher temperature.

The mixing valve in this photo adds cold to the outgoing hot water to avoid scalding, and at the same time we have more total domestic hot water for washing and bathing than if we omitted this pair of controls.

More information about tankless coils, how they work, what goes wrong, and their controls, is at Tankless Coils.

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