Combi Boiler Sequence Of Operation: From Hot Water Demand To Ignition with David Nicholson - Part 1

In this episode of the HVAC Know It All Podcast, host Gary McCreadie talks with David Nicholson, Training Manager at NTI Boilers, about on-demand water heating and combi boiler operation. They cover demand sensing, burner startup, water quality, ignition systems, and domestic hot water priority. HVAC technicians will learn how these controls work together and why a heating call does not always trigger immediate ignition.

David draws on his experience in technical support and contractor training to explain the equipment decisions behind common service questions. His work with engineering and research and development also informs his perspective on igniter reliability, while feedback from technicians helps connect product design to installation and maintenance challenges.

 

Key Takeaways

• How flow switches and flow meters signal domestic hot water demand and influence burner response.

• How the boiler checks safeties, verifies fan speed, initiates ignition, and proves flame before modulating output.

• Why incoming water filtration and water-quality treatment matter for flow-switch reliability and scale prevention.

• Why NTI Boilers moved toward spark ignition and how electrode warping can still cause failures.

• How domestic hot water priority, diverting-valve operation, and temperature differentials affect a combi boiler's response to space-heating calls.

 

Key Timestamps

00:00 – Introduction to the episode & Guest David Nicholson

02:07 – Regional differences in technician knowledge and training needs

03:22 – Learning from technicians and recognizing manufacturer knowledge gaps

10:29 – Types of flow switches, spark vs hot surface igniters, and combi

19:08 – Igniter reliability, domestic hot water priority, and space-heating controls

 

This Episode is Kindly Sponsored by:

Cintas: https://www.cintas.com/hvacknowitall

Cool Air Products: https://www.coolairproducts.net/ 

SupplyHouse: https://www.supplyhouse.com/tm 

Use promo code HKIA5 to get 5% off your first order at Supplyhouse!

 

Follow the Guest and His Company on:

David Nicholson - LinkedIn: https://www.linkedin.com/in/david-nicholson-7a9884118/

NTI Boilers - LinkedIn: https://www.linkedin.com/company/ntiboilers/

NTI Boilers - Company Website: https://www.ntiboilers.com/ 

 

Follow the Host on:

LinkedIn Profile: https://www.linkedin.com/in/gary-mccreadie-38217a77/ LinkedIn - HVAC Know It All: https://www.linkedin.com/company/hvac-know-it-all-inc 

Website: