I assume it's a thermostat problem on the Parkinson Cowan 7000 gas cooker. After lighting, the flame fires up nicely but my tenants say that even turned up fully everything they cook is taking twice as long as usual, or even longer. Could it be anything else? If the thermostat, is it straightforward to replace? Would there be a 'generic' stat available? It's an old model and maybe better to replace, but don't mind tackling a reasonably easy job, as a competent diy-er.
Hugh