A home-made app that grew to 300 users — made solid, not thrown away
The operations team of an HVAC maintenance company had built their own system: Airtable, spreadsheets and an app made with an AI app builder. It worked for 50 technicians. At 300 it crashed every week, and invoices went out nine days after the job.
- Client
- Heating, ventilation and air-conditioning service company, Poland
- Their team
- CEO (owner), the ops manager who built the original app, finance lead
- Our team
- Engagement lead, 3 engineers
- Timeline
- 6 weeks to stable · 4 months to rebuild the core
The business goal
Stop losing money between a finished job and a sent invoice — and keep the ops team able to change the system themselves.
Where it was
Technicians filled in job reports in the app; the office re-entered them into spreadsheets for invoicing. Sync conflicts lost about 30 reports a month. Nobody dared to change anything during the season.
What we did
- 1Review of what exists · 1 weekWhat to keep: the ops team’s process knowledge and screens. What to replace: data storage and sync.
- 2Stabilise · 5 weeksBackups, sync conflicts fixed, monitoring added. Crashes stopped in week three.
- 3Rebuild the core · 4 monthsOne database, a mobile app with offline mode for basements and plant rooms, an invoicing link to accounting.
- 4Run & improve · ongoingThe ops team adds forms and screens in a low-code admin; we keep the core healthy.
What did not work
Our first plan was to replace everything at once. The ops manager talked us out of it: technicians would not accept a new app in peak season. We split the rebuild and switched region by region in the quiet months.
Who did what
Before and after
Under the hood
They did not laugh at our home-made app. They kept what worked and fixed what was dangerous.