Hi,

I have a Bosch Worcester 280RSF combination boiler. I am having problems with the hot water... i.e. when I run any hot water outlet in the house, it will run hot for about 5 minutes, then temperature will drop considerably to almost cold for approximately 30 seconds, then water temperature will increase again (this process continues whilst outlet is in use).

Please help!

Regards,
Ben.

Check to see if your system has a thermostatic mixer valve on it. I would start there first.