Boiler help - hot water switch only turns on heating

[smh23]

When I turn on the hot water switch on the boiler, it actually starts the central heating instead (but does nothing to the water). The heating switch works fine, also just turning on the heating. We never use the timers, and don't think we did anything unusual to set this off.

Any ideas? Been quoted £200 by someone (who hasn't actually looked at it yet!).

 

[45yearsagasman]

Please describe your boiler and system in more detail.

 

[smh23]

It's a glowworm ultimate combi boiler. Pretty old by the looks, but not sure exactly how old.