I am struggling to find a replacement 6 bar relief valve protecting an
under counter unvented water heater.

The unit was installed by tenants and is now dribbling!

I have tried releasing water to see if grit has lodged in the seating
without success.

There are no obvious manufacturer details and general Google searches do
not lead to a supplier of parts.

This must be an item fitted with all such heaters so somebody must
supply replacements.

any ideas?
--
Tim Lamb