Five Tips to Prevent Cast Iron Boiler Failures

Our data here at HSB shows that cracked sections and low-water conditions are the two most common failure modes among cast iron boilers. These failures often cause significant financial losses and downtime of heating systems. Whether your cast iron boilers are used for hot water or steam heating applications, the following tips will help plan loss prevention steps and identify any energy efficiency improvements possible.

1. Verify Required Return Water Temperature

If the return water temperature is less than 140oF in normal operation, corrective steps should be taken.

  • Make sure the boiler is not deviating from the operating temperature limits specified by the manufacturer. This includes proper sequencing and activation of heating zone valves or pumps.
  • Verify operating supply temperatures, burner turndown rates, lower limits of outdoor-reset control, and proper use and maintenance of return-water mixing valves.

Maintaining the minimum return-water temperature is especially important for hot water boilers. For steam boilers, the low return-water temperature issue is less critical. Most cast iron boiler manufacturers require the return-water temperature to be above 140oF.

2. Perform Regular Low Water Cut Off Tests and Bottom Blowdowns For Steam Boilers

The most effective way to prevent low-water losses is to test the cut off devices regularly. This will identify any malfunctioning and allow for repair or replacement of the device.

Steam heating boilers typically use a float for the primary control. Testing is especially important for float type devices.

  • This is due to the sludge and mineral deposits that can accumulate inside the float chamber and impair the proper movement.
  • Float devices should be blown down and tested regularly to flush out contaminants.
  • Refer to the manufacturers’ instructions for test methods and test frequencies.
  • A boiler log should be kept to track maintenance.
  • Bottom blowdowns can be used to flush out the sediment deposits that accumulate from freshwater added. Steam boiler bottom blowdowns should be performed per boiler manufacturers’ instructions.

3. Prevent Short Cycling

Boilers are controlled to their setpoints by burner modulation or by cycling the burner on and off. For on-off control, firing cycles at 4-6 times per hour is an optimum range.

Higher firing cycles represent a condition called “short-cycling.” Short-cycling can increase fuel costs and may equipment failure.

  • Short cycling is caused by a mismatch between the amount of heat needed in the building and the size of the boiler. Warmer than usual heating seasons can cause this to happen more often.
  • Boilers that experience short-cycling should be evaluated to see if a different boiler size is needed for the area.
  • A proper annual tune-up of the boiler and heating system should always follow the manufacturer’s recommendations and be performed by qualified persons.

4. Monitor Makeup Water Tanks and Condensate Return Tanks

Steam heating boilers are normally equipped with feedwater tanks and condensate return tanks. Tank and pump leakage and malfunctioning controls can cause water damage and property loss.

Makeup water tanks can provide clues to the heating system’s health.

  • The amount of freshwater within the tank should be tracked.
  • Watch for large amounts of water usage.
  • Watch for a large condensate return temperature drop across the tank. Both of these indicate a large system leak. Any leaks should be identified and repaired.

5. Utilize Realtime Monitoring

If your energy management system does not already provide remote monitoring capabilities, please contact HSB for help. HSB Connected Technologies can provide the latest IoT sensor technologies for property loss prevention and provide insights into effective boiler system management.


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© 2020 The Hartford Steam Boiler Inspection and Insurance Company. All rights reserved. This article is for informational purposes only and is not intended to convey or constitute legal advice. HSB makes no warranties or representations as to the accuracy or completeness of the content herein. Under no circumstances shall HSB or any party involved in creating or delivering this article be liable to you for any loss or damage that results from the use of the information contained herein. Except as otherwise expressly permitted by HSB in writing, no portion of this article may be reproduced, copied, or distributed in any way. This article does not modify or invalidate any of the provisions, exclusions, terms, or conditions of the applicable policy and endorsements. For specific terms and conditions, please refer to the applicable endorsement form.


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