Homes with microbore pipework: what it means for upgrades
Microbore pipework — narrow pipes typically feeding radiators from a manifold — was popular in heating retrofits from the 1970s onwards because it was quick and cheap to install through timber floors. It behaves differently to modern larger-bore pipework in ways worth understanding before a boiler upgrade.
What is actually going on with microbore pipework
Microbore's smaller internal diameter restricts flow rate compared with 15mm or 22mm pipework, which can limit how quickly radiators heat up and how well a modern high-output boiler is matched to the existing distribution system. Some microbore systems perform perfectly well when paired with the correct pump settings and a boiler suited to the system, while others benefit from selective pipework upgrades on the worst-affected radiator circuits.
Practical notes on microbore pipework
- Microbore has a smaller internal diameter than standard 15mm or 22mm pipe
- Reduced flow can slow radiator heat-up time on some circuits
- Correct pump speed setting matters more on a microbore system
- Not all microbore needs replacing — some systems perform adequately as is
- Manifold connections are checked for condition during a survey
Where we deal with this
Who should undertake the work
- Gas appliance work must be completed by a suitably qualified Gas Safe engineer
- Oil appliance work should be completed by a suitably qualified OFTEC technician
- Jamie Crawford Heating states both Gas Safe and OFTEC registration
Need help with microbore pipework?
The honest position: Microbore pipework isn't automatically a problem — each circuit is assessed on its own performance before deciding what, if anything, changes.
Use the enquiry form to describe the appliance, fault code and what changed before the problem started.
Related help pages
- Property typeExternal oil boiler siting: clearances and weatherproofing
- Property typeHard-water Mendip properties: protecting the system long term
- Property typeHeating converted barns: open volumes and long pipe runs
- Property typeHeating large rural houses: zoning and boiler capacity
- Efficiency controlsWeather compensation: adjusting flow temperature to the outdoor climate
- Oil tank checksWhy the oil tank gets inspected as part of a boiler service
Services that cover this
Questions we get asked
- Does microbore need replacing when the boiler is upgraded?
- Not always — it's assessed circuit by circuit, since some runs perform fine while others may benefit from upgrading.
- Can a modern boiler work with microbore pipework?
- Often yes, with the right pump settings, though this is confirmed during the survey rather than assumed.
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