Requirements When Installing a Boiler

With older, lower efficiency cast iron boilers, water chemistry was generally not a major concern. However with today’s higher efficiency modulating/condensing boilers, water quality is a concern.

These new boilers have much smaller water volumes and are constructed from metals much different than cast iron and therefore must be protected.

Recommended steps for installation of a new or retrofit boiler:

  1. Flush the system with clean water.
  2. Isolate the boiler and fill the system with fresh water and a boiler cleaner. (Utica and Bosch recommend Sentinel X-300 for new systems or X-400 for existing systems). Do not use TSP (tri-sodium phosphate) and under no circumstances should any boiler cleaner be pumped through the new boiler.
  3. Run the pumps for 30 minutes to an hour.
  4. Thoroughly flush the system with fresh water. Ensure all loops are flushed and drained.
  5. Eliminate any system leaks. The addition of make-up water will constantly introduce oxygen and minerals that will damage the boiler. Fill water pH must be maintained between 7 and 8.5; water hardness should be at 7 grains per gallon or less, and chlorine level must be 100 ppm or less.

Fill Water

Do not use water treated with salt bedding type water softeners. Tap water may be used. If it exceeds a pH of 8.5 or a hardness of 7 grains per gallon or higher, it must be pre-treated. Sentinel X-100 Inhibitor can be used if the pH is below 7.

For water hardness higher than 7 grains per gallon it can be demineralized by pumping it through a de-mineralizer, such as manufactured by Axiom. Another option would be to purchase distilled water from a local water supplier.


Follow the boiler manufacturer’s recommendation for any specifics on anti-freeze. Typically they will recommend an inhibited propylene glycol. Corrosion inhibitors vary by the metals they are designed to protect, and the boiler manufacturer may recommend specific brands.

The source for this Tech Tip: Buderus Technical service bulletin “Boiler Water Chemistry and Freeze Prevention Guidelines

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