Honeywell heating zone valveDissolved Oxygen Damage to HVAC Equipment
Cause & Prevention of hydronic or HVAC system damage by dissolved oxygen

  • DISSOLVED OXYGEN DAMAGE CONTROL - CONTENTS: what are the causes of damage to hydronic (hot water) heating pipes, controls, zone valves, other valves caused by dissolved oxyten in the heating system water? how to reduce the risk of heating system component or pipe damage from dissolved oxygen
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Dissolved Oxygen problems in hydronic heating systemsd:

What is a zone valve, how do they work.

How do I choose & install a zone valve, how do I wire up a zone valve, and how do I troubleshoot, repair or replace a zone valve?

This article series 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 few zone valves controlling heat distribution in U.S. home. Some manufacturers such as Honeywell specifically warn against using some zone valves on heating systems where a significant level of dissolved oxygen is likely to be present.

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Dissolved Oxygen in Heating Boiler Water: Problems / Remedies

LARGER VIEW of a heating boiler cad cell relay switch

Watch out: Hydronic heating system (hot water) heating boiler zone valves, pipes, controls, or the boiler itself may suffer a reduced life or damage from signifcant levels of oxygen dissolved in the heating system's water.

Several corrosive effects may be present, including highly-corrosive water, improper pH, and heating system water with a high oxygen content.

Question: are there zone valves that resist damage from dissolved oxygen in hydronic heating system boiler water

Denys Picard said:

Honeywell warns that makeup water feed to a boiler may damage the rubber plug of Zone Valves 8043 and make them fail.

Are they zone valves resistant to dissolved oxygen from makeup water feed? Thank you. - question and reply posted originally at ZONE VALVE DIAGNOSTIC FAQs


Thank you for a great question, Denys. In the Honeywell company's product literature for some products we read:

Suitable for glycol/water mix up to 50:50 use in closed hydronic systems. Not for use with oxygenated water, potable water or steam.

Use this valve in hydronic systems which do not contain dissolved oxygen in the system water. The dissolved oxygen, which is found in systems that have a frequent source of make-up water, causes the rubber plug inside the valve to deteriorate and eventually fail. - sources given below.

I have had trouble finding residential-grade zone valves that specifically claim extra resistance to dissolved oxygen in the heating water [I'm still researching that option].

But beyond warnings supporting your concern, I also found a different viewpoint arguing that in an intact (not leaky) closed residential hydronic heating system, the dissolved oxygen in the initial water fill is not likely to be enough to raise a corrosion problem. So why the warnings?

I speculate that warnings from Honeywell, Taco, and other manufacturers of heating equipment are based on a more-practical observation that over the life of a typical residential hydronic heating system both corrosive water or system water and air leaks are common enough that dissolved-oxygen-related parts corrosion can lead to failures of zone valves or other components.

We report here on the common measures recommended to avoid heating equipment or control or piping damage from dissolved oxygen.

Dissolved Oxygen Hazards for Hydronic Heating Systems

The chief oxygen corrosion hazard for residential zone valves would be in using this zone valve on a hot water heating loop supplied from a steam boiler - perhaps for heating a basement or lower building floor when other areas are heated by steam. Because steam boilers continually require makeup water the water chemistry is a concern for the zone valve as well as for other parts.

A straight 100% hydronic (all hot water) heating system is not normally taking in makeup water; even so, some experts note that both dissolved oxygen and low pH in these systems are principal causes of component corrosion. - That source suggests (and discusses the pros/cons of ) using a deaerator or an economizer to reduce the dissolved oxygen level if your system is suffering from that problem.

That's from a (in my OPINION) rather reputable source that I've cited before, GE Power Water & Process Technologies, a division of General Electric, that sells water treatment equipment (perhaps of particular concern for large commercial plants or power generating plants).

We researched oxygen related corrosion in residential hydronic or hot water heating systems, finding that the presence of legionella bacteria was cited more often than corrosion concerns for the water in these systems.

If you are eliminating air from your system properly you are probably reducing the dissolved-oxygen-related risk for residential hydronic heating systems. (Cotton 2013).

In my OPINION was supported by Larsen's work back in 1975: if your closed-system hot water (hydronic) residential home heating boiler is not suffering from recurrent air problems, oxygen corrosion should not be a significant worry.

Here is an Except from Larsen on oxygen dissolved in home heating system water:

Were water of this same oxygen concentration [as distributed in a municipal water supply, up to 14 mg/l] used in a home hot-water heating system largely composed of steel with no replenishment or replacement of the water, the system would last indefinitely, because the limited supply of oxygen would be quickly removed, and little or no corrosion would then be possible.

Watch out: the final authority about the requirement to avoid dissolved-oxygen damage is the manufacturer, such as Honeywell if you are using a Honeywell product. For certain products the company specifically warns "not for use in systems containing dissolved oxygen". Examples include:

You should call the manufacturer to ask if your specific system set-up is a concern or not. If you don't have it, contact information for Honeywell is at HONEYWELL CONTROLS.

Larsen's study concludes with this warning worth noting, while keeping in mind that here the focus was not specifically on heating boilers:

The determination of the depletion of dissolved oxygen throughout this system is not a true measurement of the degree of corrosion.

Depletion of dissolved oxygen at the “dead” ends and service lines of the [public water distribution] system gives rise to a condition where ferrous iron is not oxidized to insoluble ferric oxide and solution of iron to the ferrous state takes place at the expense of the nitrite and nitrate previously formed—quite possibly by bacterial action.

What corrosion that does take place in the system as a whole is magnified by the accumulation of traces of the iron in the gelatinous masses of bacterial growths clinging to the pipe in localities where the velocity of flow is low and sloughing off occasionally.

Methods for Avoiding Dissolved Oxygen Damage to HVAC Equipment, Piping Controls

Air scoop air purger air separator (C) Daniel Friedman

Research on HVAC Equipment or Control Damage from Oxygen Dissolved in System Water Supply


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