Renovating an old house, we found the cold washers were rubber and the hot washers were fibre. Presumably because the rubber expanded with 60 celcius water. Now every brand I see claims to be suitable for hot and cold. Are they all low-expansion materials nowadays?
They must be very old. Many decades now since hot and cold taps had different washers. (1950s?) At one time CW taps had leather washers and HW had some sort of fibre last didn't last long. Also CW taps had loose "jumpers" and HW taps had fixed ones.
Maybe the cold washers had failed and had been replaced.
Probably just that the cold washers wore out before the hot.
Modern ones are probably EPDM, a synthetic rubber that is both WRAS approved and rated to 85C. WRAS approved natural rubber products are mostly rated to 23C or 30C.
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