My Vaillant Turbomax 28 just received a service and now there is no hot water, heating works fine now.

The boiler engineer has come back, looked at it and said he would come back Monday. He undid the valve that regulats the waterflow to radiator/hot water and that is working.

Bit miffed as it is weekend and we can;t take a hot shower.

Any tips how to rectify this myself?