The verdict in three sentences
For an HVAC maintenance business with 35 engineers, moving from a whiteboard to a field service app frees roughly 45 minutes per engineer per day, over 5,700 hours a year. A SaaS at GBP 30-52 per engineer per month works if your contracts are standard, but it costs GBP 12,600 to 21,800 a year and you never own it. A custom app at GBP 26,000-47,000 pays back in under three years once you have bespoke maintenance contracts, F-Gas obligations or complex invoicing.
Where the 45 minutes a day go
Whiteboards and paper job sheets create hidden losses: calls to the office for the next address, trips back to the depot to drop off sheets, re-keying by admin staff, photos sent on WhatsApp and then lost. Here is the breakdown observed at maintenance firms with 20 to 50 engineers.
| Source of loss | Whiteboard and paper | With the app | Daily saving |
|---|---|---|---|
| Calls to the office about the schedule | 15 min | 3 min | 12 min |
| Filling in and dropping off job sheets | 20 min | 6 min | 14 min |
| Looking up equipment history | 10 min | 2 min | 8 min |
| Sending and filing photos | 8 min | 1 min | 7 min |
| Poorly optimised routes | 12 min | 8 min | 4 min |
| Total | 65 min | 20 min | 45 min |
Across 35 engineers and 220 working days, that is 5,775 hours. Even valuing only half of that time at GBP 40 per billable hour, the gain exceeds GBP 115,000 a year in extra job capacity (2026 estimate). In the office, invoicing moves from day 12 to day 2 on average.
Custom or SaaS: five-year comparison
| Criterion | Field service SaaS | Custom |
|---|---|---|
| Upfront investment | GBP 1,700 to 4,300 setup | GBP 26,000 to 47,000 |
| Recurring cost (35 engineers) | GBP 12,600 to 21,800/year | GBP 4,100 to 6,200/year maintenance |
| Total cost over 5 years | GBP 64,700 to 113,300 | GBP 46,500 to 78,000 |
| Time to go live | 1 to 2 months | 4 months |
| Offline mode (plant rooms, basements) | varies by vendor | designed in from day one |
| F-Gas refrigerant log | rarely native | built in |
| Job sheets in your own format | partial | full |
| Code and data ownership | no | yes |
SaaS stays relevant below 15 engineers or to trial digitisation for a year. Above 25 engineers, cumulative licence fees overtake the custom investment from year three.
What a GBP 26,000-47,000 app includes
The GBP 26,000-33,000 version covers a drag-and-drop schedule for the office, a mobile PWA for engineers with offline mode, on-screen signed job sheets, geotagged and timestamped photos, and equipment history via QR code. The GBP 39,000-47,000 version adds maintenance contract management with automatic preventive visits, the F-Gas log, van stock management and a link to your invoicing software (Xero, Sage or QuickBooks).
The project takes four months: 3 weeks of on-site scoping with two engineers, 10 weeks of development, then a 3-week pilot with one team before company-wide rollout.
Mini case study
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James, managing director of a 35-engineer HVAC maintenance firm in Birmingham, is weighing a SaaS at GBP 41 per engineer per month (GBP 17,220 a year) against a custom app at GBP 40,000 with GBP 5,200 of yearly maintenance. Over five years, the SaaS costs GBP 86,100 plus GBP 3,500 setup, or GBP 89,600. The custom app costs 40,000 + 26,000 = GBP 66,000. The gap is GBP 23,600 in favour of custom, and the built-in F-Gas log saves a second tool at about GBP 2,000 a year.
FAQ
How much does a field service app cost in the UK in 2026?
A custom app costs GBP 26,000 to 47,000 depending on scope, plus GBP 340 to 520 a month for maintenance. An equivalent SaaS charges GBP 30 to 52 per engineer per month.
Does the app work without signal?
Yes, offline mode stores the day's schedule, equipment records and job sheets on the phone. Sync happens automatically when signal returns, usually in under 10 seconds.
Will engineers actually use it?
Adoption depends on simplicity: a job sheet must take under 3 minutes to complete. The 3-week pilot with one team lets us adjust the interface before rolling out to all 35 engineers.
Do we need to buy tablets?
No, the app runs as a PWA on the Android or iPhone handsets you already issue. For a new fleet, budget GBP 220 to 350 per rugged device.
Is a signed digital job sheet legally valid?
A timestamped on-screen signature with photos is strong proof that the work was carried out. It is archived as a PDF and emailed to the customer in under a minute.
Let's scope your project. Tell us your number of engineers, contract types and invoicing software: we will price an app between GBP 26,000 and 47,000 delivered in four months, with a five-year SaaS comparison. 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.
