Two bathrooms and poor flow: diagnosing the real bottleneck

Things worth knowing about poor flow across two bathrooms

• Combi boilers have a maximum simultaneous hot water flow rate
• Undersized distribution pipework restricts flow independent of the boiler
• Incoming mains pressure is measured before assuming a boiler is at fault
• A system boiler with a cylinder handles simultaneous demand differently to a combi
• Shower type and flow restrictors also affect the flow a household actually feels

Where poor flow across two bathrooms usually comes from

A combi boiler has a maximum flow rate it can heat at any one time, so simultaneous demand from two showers can genuinely exceed its capacity, in which case a system boiler with a cylinder or a boosted stored system is worth considering. Equally, undersized distribution pipework or naturally low incoming mains pressure can restrict flow regardless of boiler size, so flow and pressure are measured at source before deciding what to change.

Where we deal with this

• Bath (BA1) · 8 mi
• Westfield (BA3) · 1 mi
• Warminster (BA12) · 15 mi

Questions we get asked

Does upgrading the boiler always fix two-bathroom flow issues?

Not necessarily — pipework and incoming pressure need checking too, since a bigger boiler cannot fix a restricted pipe run.

Would a cylinder-based system suit two bathrooms better?

Often yes, since stored hot water isn't limited by instantaneous heating capacity the way a combi is.