11. Understanding Block Vent Safety Spill Switch on Hydronic Gas Boilers

Ever wonder what actually happens when a chimney gets blocked on a hydronic gas boiler? In this hands-on training session, Mikey Pipes demonstrates a real-world spill switch activation on a US Boiler Series X-2 cast-iron boiler—showing exactly how the blocked vent safety protects the home.

This is Episode 11 in our hydronic heating training series, and today we walk through:

🔥 What the blocked vent switch (spill switch) does
🔥 How it reacts when exhaust gases spill from the draft hood
🔥 What temperatures trigger the safety
🔥 How to verify a tripped spill switch with a multimeter
🔥 How the boiler reacts: STA codes, damper operation, lockout, and reset
🔥 Real-life scenarios: collapsed terracotta liners, downdrafts, tight homes, exhaust fans & more

If you're training for the HVAC/plumbing trade or brushing up on hydronic boiler safeties, this is a MUST-WATCH demonstration loaded with real-world knowledge you won’t find in the classroom.

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We break down boilers, hydronics, primary/secondary piping, combustion, safety controls, heat exchangers, and everything today’s techs MUST know to level up in the field.

⏱️ Chapters

00:00 – Intro & System Overview (US Boiler X-2)
00:18 – Boiler Operating Conditions (Temps & STA Codes)
00:35 – Blocking the Chimney Exhaust
00:58 – Spill Switch Trips (Safety Activation Sound)
01:20 – Boiler in Standby With Active Call for Heat
01:45 – Testing Spill Switch Continuity (Fluke 116 Demo)
02:20 – Resetting the Spill Switch & Damper Operation
02:48 – STA Sequence: Prep → Spark → Flame Proving → Running
03:10 – Why a Spill Switch Trips (Real-World Failure Scenarios)
04:00 – Downdrafts, Tight Homes & Exhaust Fan Effects
04:21 – Final Explanation: How the Spill Switch Protects Life & Property

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#HVACtraining #BoilerSafety #MikeyPipes