I'd pay to use the forum, but since I'm tending to give more advice than I ask for, I don't expect to pay a lot.
When I was a member of 2CVGB, the forum was included in annual membership (currently £34 a year and includes the cost of printing and posting a monthly colour magazine), so £24 (£1.99 a month) for plumbersforums seems extremely dear.
As far as the forum itself goes, there no longer seems to be a non-gas boiler or even a heating category that isn't for RGIs, so questions like 'What temperature should I run my boiler at?' or 'Will a programmable thermostat really save energy?' can only really go in the general plumbing section, which seems odd when we consider the number of niche categories that DO exist. Perhaps this could be rationalised somewhat?