Why is diagnostic separate from repair labor?
A customer who chose repair over replacement wants to see that the fix was the cheaper path. Showing the diagnostic and the labor separately does that.
Water heater · Free invoice sample
The general shape of a water heater or boiler service invoice — the recurring maintenance or repair visit, not the replacement. Diagnosis, labor, parts, and safety items broken out so a customer sees what was done and why.
Common practice
Water heater calls turn into replacement conversations. The invoice should make it clear which one this was.
A customer who chose repair over replacement wants to see that the fix was the cheaper path. Showing the diagnostic and the labor separately does that.
Relief valves, expansion tanks, and venting checks are cheap and easy to skip. Listing them shows the customer the visit covered safety, not just the symptom.
So nobody reads this invoice as a warranty on the heater. It bounds your responsibility to the work you did.
Before you send it
Water heaters sit at the intersection of plumbing, gas, and building code. What you're allowed to touch, and what needs a permit, varies.
General information, not legal, tax, or licensing advice. Requirements differ by state, county, and city and change over time. Confirm with your state licensing board and the local authority having jurisdiction before relying on any of this.
Estimator notes
No. Note that a replacement estimate was provided separately. Mixing them makes the repair look like a down payment on a sale.
Rarely for part replacement; usually for full unit replacement. Check locally and don't guess on gas work.
Bill labor and note the part was supplied under manufacturer warranty at no charge. Customers appreciate seeing the zero.
Annually is the standard recommendation. Say so on the invoice — it's your next call.