The instinct to pay cash
Most people's instinct is to pay cash if they have the money available — "why take on debt if you don't need to?" It's a reasonable instinct, but financially suboptimal when the debt is at 0% interest.
The maths of 0% finance
A £1,299 boiler on 36-month 0% finance = £36.08/month. If you have £1,299 in a savings account earning 4.5% interest: you earn approximately £175 over 36 months while paying back £36/month. You're £175 better off by using 0% finance.
The case for cash
Cash makes sense if: you have no savings (using 0% finance prevents depleting emergency funds), you strongly dislike any form of debt, or your savings earn no interest.
What about higher-interest finance?
Our finance is specifically 0% — which is very different from high-interest hire purchase or personal loans (10–30% APR). The 0% rate is the key factor that makes the maths work in finance's favour.
Verdict
If you have savings earning any interest: 0% finance is technically the better financial choice. If you have no savings: use 0% finance to keep your emergency fund intact. Cash is only clearly better if you have no savings account and genuinely dislike debt.