Hi.....I experienced same issue.........I called out the Grant engineer who explained to me,.......
The Grant Combi oil boiler is hot water priority......when the boiler starts, it will run with hot water only, until the hot water supply is up to temperature. Then the heating kicks in.
So wait...
Most of the people who buy my repair kit are private individuals.......who repair their own pump.
I have repaired several successfully...if the gear wheel slots are not damaged, the repair is permanent. My CNC manufactured carbon steel drive pegs are very robust and last, unlike the original...
Hi
Yes there is difficulty when trying to re-assemble the Riello pump.
Check on ebay......I am posting a Riello repair kit, with full repair instructions. This includes how to avoid the problem you experienced.
Macrut.