A locator that documents format, not just location
Most manufacturers publish a diagram showing where the rating plate is. Triangle Tube's Serial Number Locator goes further: for each product family it gives the location of the serial number and the shape of the number itself, with worked examples. That combination makes the page the reference for identifying which generation of a product is installed before parts or documents are ordered.
The company ceased operations on November 3, 2025, and its site states that spare parts are being made available through stocking distributors while they remain available. That makes accurate serial identification more important, not less, because parts have to be matched correctly the first time from the records that remain.
The Prestige families: PA, PT and PS
For the Prestige PA boiler, the locator says to look toward the bottom of the right side panel. The serial begins with PA, PB or PEA followed by six digits, and the page gives the examples PA123456, PEA123456 and PB234567. For the Prestige PT, the front panel has to be removed; the serial is then visible and takes the form PT followed by seven digits, for example PT1234567. For the Prestige PS, the flap on the front of the unit is opened and the number is found on the bottom of the flap tab, formatted as PS followed by four or five digits, for example PS1234 or PS12345.
Those prefixes are not cosmetic. They are the production-generation identifiers that separate one build of the Prestige platform from another, which is why the recall described below is defined by prefix and manufacture window rather than by model name alone.
Instinct, Ionic and Cardinal: plate locations
For the Instinct Floor and Instinct Wall boilers, the locator places the serial toward the top of the right side panel. The Ionic Floor Standing unit carries it toward the bottom of the right side panel, the Ionic Wall Mount toward the upper right side panel, and the Cardinal at the top of the unit.
Instinct documentation adds a second layer. The published application guides are selected by the characters in the serial number that follow the S or C: one guide covers units with AA or no letter after S or C, and separate guides cover units with AB after S or C. A technician choosing between those guides reads the serial first, because the correct wiring, settings and service information depend on the revision the number identifies.
Challenger, Marquis and Keystone formats
The remaining lines have their own documented shapes. A Challenger serial is six digits, a dash, then ten alphanumeric characters, with the locator giving 012345-1234A56789 and 012345-1234567890 as examples. The number sits toward the top of the right side panel. A Marquis serial is found in the middle of the large sticker on the right side panel and starts with TH followed by seven to nine alphanumeric characters, for example THN1234567 or THP1234567B. A Keystone serial is on the large sticker on the right side panel and starts with K followed by eight digits, for example K12345678.
Read together, the page shows that Triangle Tube serials are self-describing at the family level: the leading letters or the presence of a dash tell a technician which product and which format they are holding before any database lookup happens.
The serial number in the 2025 recall
Triangle Tube's 2025 product recall covers Prestige Solo, Prestige Excellence and Aerco Esteem condensing gas boilers manufactured between December 2011 and April 2019. The company identifies affected units by serial number prefix: AE, PT, PA, PTE and PEA. The recall notice states that the recalled boilers can release carbon monoxide because of delayed ignitions or component damage, which is why the identification step is a safety step, not an administrative one.
Owners who believe their boiler may be in scope should use the manufacturer's recall page to check the serial and register, and should treat any combustion or carbon-monoxide symptom as an emergency. The serial number is the only reliable way to determine eligibility; model name alone does not distinguish the affected production window.
What a technician does with the number
Four jobs depend on the serial. Recall screening compares the prefix and, where needed, the production record against the December 2011 to April 2019 window. Documentation matching uses the Instinct revision letter after S or C to select the right application guide. Parts ordering uses the family prefix to confirm which generation of a component fits. And warranty work requires the serial: the warranty claim process is built around it.
The practical routine is to photograph the rating plate on the first visit and record the serial in the service history. On a discontinued brand with a distributor-based parts supply, that photograph is often the difference between a one-visit repair and a week of back-and-forth.