When the boiler fails, many homeowners face a choice: replace just the boiler, or take the opportunity to upgrade the full system including radiators, pipework, and controls. Here's how to decide.
Just replace the boiler if:
- Your radiators are correctly sized and in good condition
- Your pipework is modern 15mm/22mm copper (not microbore)
- Your controls are relatively modern (last 10 years)
- Your system has been power flushed and has a magnetic filter
- Budget is the primary consideration
Consider a full upgrade if:
- Radiators are old or clearly undersized (cold spots, rooms that don't heat)
- You have original 1970s/80s microbore pipework (8mm or 10mm)
- You've been wanting a different boiler type (e.g., combi to system or vice versa)
- You have no TRVs on radiators
- You want smart heating controls installed properly from the outset
The cost difference
Boiler-only: £1,099–£1,799. Full system (boiler + all radiators): £2,500–£6,000+. Full system with smart controls: £3,000–£7,000+.
The payback argument
New radiators with correct sizing and TRVs can reduce bills by 15–20% vs old undersized radiators. On a £1,100 gas bill, that's £165–£220/year — a 3–5 year payback on the radiator upgrade cost.
Our recommendation
We always assess the full system during our free survey and give you honest advice on what genuinely needs replacing vs what's fine to reuse. Book your survey.
#replacement#system upgrade#radiators#planning