Methodology

Every code meaning and every default number on this site comes from a document you can open yourself. This page explains how those documents turn into pages.

Error codes

We start from the manufacturer's current U.S. installation and operation manual and owner's manual for each model series, and note the document title, its revision or date, and the page where each code appears.

The meaning at the top of a code page is the manufacturer's wording, in quotation marks, with the document and page. When two manuals word a code differently, both versions are shown.

The checks listed for the owner are the ones the manual describes and that do not involve gas parts: confirming the gas and water supply are on, looking at the vent outside, cleaning a filter where the user's manual shows the owner how. Some of those filters sit behind the front cover (Navien's air intake filter is one), and we include that step only when the user's manual gives it to the owner. Other work inside the unit, on the gas valve or burner, or on the circuit board is marked for a licensed technician.

If a page mentions a cause the manual does not list, it says where that cause comes from. Forum posts never define what a code means.

A code gets its own page only when the manual gives enough to build a useful check. Every other code is in the brand's full table with its meaning and source.

Calculators

Each calculator page shows the formula, the default values and the source of each value. The defaults can be edited: a number from your appliance's nameplate or spec sheet is better than any chart. The calculation code is kept apart from the page and is tested against worked examples. Each calculator also lists what it leaves out.

Calculators so far: generator size.

Keeping pages current

Manuals get new revisions; rules and prices change. Pages that depend on them sit in an update queue with a re-check date. When a re-check finds a change, the page is updated, and if the change fixes an error it is logged on thecorrections page.