The
idea is great. The problems will be with the implementation, how it will change incentives, any loopholes introduced, cost of enforcement and unintended consequences.
What exactly is a repair? Are parts covered, or only labour? Think ship of Theseus. Is an upgrade a repair, can I put a better compressor, rather than like-for-like in my refrigerator when it's failed? Can I have my TV repaired by replacing all the parts, except the power cord? How broken must something be before it can be repaired? Totally failed, failure imminent, or just worn? (Unintended consequence: people have their things fixed long before it's strictly necessary, leading to greater waste than if they'd just let the thing fail and bought a new one. Another one: appliances are only upgraded to newer, much more energy efficient ones much later than otherwise).
And for labour, where is the line drawn? Is the labour cost of diagnosing a problem covered? What if the problem is bigger than expected, and it isn't economical to carry out the repair? What if I have you upgrade the Foo (not a repair), which is trivial, while you've taken the widget apart anyway to fix the Bar (a repair)? What about repairing something, pocketing the tax break, then selling it (perhaps outside of the country)?
Once you have considered all of these questions, you either have a lot of loopholes which will make the tax break much more expensive, or have a very long body of legal texts, and some very exited lawyers and auditors which will impose an indirect cost on society broadly.
Sure, it's pessimistic, but I'm essentially working backwards from an attempt to impose a tax on dietary fat (for health reasons) in Denmark. Sounds great, right? Hilarity ensued over mixed nuts (the accountants had a field day with that one, and IIRC all kinds of meat being taxed at the same level, and the tax was repealed after only 15 months.