The verdict in three sentences
For an HVAC maintenance firm with 25 engineers, a field service app replaces phone scheduling and paper job sheets, and moves invoicing from day 12 to the same day. In Manchester, a custom PWA costs 30,000 to 50,000 GBP (28,000 to 45,000 EUR for a Bordeaux build), while off-the-shelf SaaS charges 45 to 80 GBP or EUR per engineer per month, i.e. 13,500 to 24,000 a year. Custom pays off from year two or three, sooner if your maintenance contracts have rules that standard software handles poorly.
What paper job sheets cost
An HVAC company of this size carries out about 9,000 jobs a year: planned preventive maintenance under contract, reactive call-outs, commissioning. Two coordinators schedule by phone, engineers fill in a paper job sheet signed by the customer, sheets come back to the office at the end of the week, then are re-keyed for invoicing. The result: 12 days on average between the visit and the invoice, 3 to 5% of sheets lost or illegible, and customer disputes for lack of a photo or proven arrival time.
| Indicator | Paper job sheets | With the app | Change |
|---|---|---|---|
| Visit to invoice | Day 12 | Same day | −12 days |
| Lost or incomplete sheets | 3 to 5% | Under 0.5% | −90% |
| Office re-keying time | 3 min per sheet, 450 h/year | 0 | −450 h/year |
| Scheduling calls per day | 60 to 80 | 20 to 30 | −60% |
| Jobs per engineer per day | 3.2 | 3.6 | +12% |
| Disputes over whether work was done | 8 a month | 1 to 2 a month | −80% |
| Average debtor days | 52 days | 40 days | −12 days |
Custom PWA vs off-the-shelf SaaS: a 5-year comparison
| Criterion | Field service SaaS | Custom PWA (Manchester) | Custom PWA (Bordeaux) |
|---|---|---|---|
| Entry cost | 2,000 to 6,000 setup | 30,000 to 50,000 GBP | 28,000 to 45,000 EUR excl. VAT |
| Recurring cost for 25 engineers | 45 to 80/engineer/month, i.e. 13,500 to 24,000/year | 600 to 900 GBP/month maintenance | 500 to 800 EUR/month maintenance |
| 5-year cumulative cost | 70,000 to 126,000 | 66,000 to 104,000 GBP | 58,000 to 93,000 EUR |
| Go-live time | 4 to 8 weeks | 3 to 4 months | 3 to 4 months |
| Offline mode (plant rooms, basements) | Varies by vendor | Designed in from day one | Designed in from day one |
| Contract rules (PPM schedules, SLAs, call-out cover) | Limited configuration | Modelled exactly | Modelled exactly |
| Integration with existing invoicing (Xero, Sage) | Standard connectors | Built for your tool | Built for your tool |
| Scaling to 40 engineers | Cost grows per seat | Near-fixed cost | Near-fixed cost |
SaaS remains the right choice to start quickly with a standard process. A custom PWA is justified when the company has complex contracts, an invoicing system to keep and growth plans that would make per-seat pricing heavy.
Typical functional scope
Office side: drag-and-drop scheduling, assignment by skills (F-gas certification, electrical qualifications), automatic generation of planned visits from contracts, parts tracking. Engineer side, on a smartphone: today's jobs, route, asset history, checklist per equipment type, before/after photos, readings (pressures, temperatures, refrigerant quantities for the F-gas log), customer signature on screen and a PDF job sheet sent immediately. Offline mode is essential: data syncs when the network returns, with no loss. The 3 to 4 month plan includes 3 weeks of scoping with 3 engineers, 8 weeks of development and a 3-week pilot with one team.
Mini case study
Julien runs a 25-engineer HVAC maintenance firm in Bordeaux with 3.4 million EUR of revenue. He invests 38,000 EUR in a custom PWA plus 650 EUR a month of maintenance. The 450 hours of re-keying removed are worth 13,500 EUR a year. The 12 debtor days saved on 3.4 million EUR free about 110,000 EUR of cash, or 4,400 EUR a year of interest avoided at 4%. The 4% of jobs never invoiced, brought down to 0.5%, represent about 35,000 EUR a year recovered on reactive work. Annual gain: close to 53,000 EUR, against a first-year cost of 45,800 EUR. The app pays back in 11 months. A Manchester firm of the same size paying 42,000 GBP sees a similar payback, as UK labour costs raise the value of every hour saved.
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FAQ
How much does a custom field service app cost in 2026?
In Manchester, expect 30,000 to 50,000 GBP; in Bordeaux, 28,000 to 45,000 EUR excl. VAT for a PWA with scheduling, offline mode, signature and photos. Maintenance then costs 500 to 900 a month.
Why a PWA rather than a native app?
A PWA installs from the browser on Android and iPhone without going through app stores, and costs 30 to 40% less than two native apps. It handles offline mode, the camera and signatures.
What happens when the engineer has no signal?
All of the day's data is stored on the phone. The job sheet is signed and saved locally, then synced automatically as soon as the network returns, usually within 30 seconds.
How long is the rollout?
3 to 4 months, including a 3-week pilot with a team of 5 engineers. Training an engineer takes about 1 hour.
Can we keep our invoicing software?
Yes, the app sends approved job sheets to your existing invoicing tool by API or export. The invoice goes out the same day, with no re-keying.
Let's scope your project. An offline field service PWA for 25 engineers with signature, photos and same-day invoicing, indicative budget of 38,000 EUR (about 32,500 GBP), rolled out in 3 to 4 months. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
