There are 2 non return valves one in CH direction and one in DHW direction (pump is next in line), turned boiler off, isolated cold mains feed and ran tap, tap stopped. (so I assume its not stuck open!)
Also rechecked flow switch by disconnecting, DHW pump carries on running.
Hi, its a Grant Vortex Condensing Combi 26 (2006/2007 year)
Flow switch checks out fine.
Pressure switch checks out fine.
Both thermistors checked out fine.
Blend valve removed and refitted (hardly any limescale)
Since then I found a relay which controls the DHW pump had burn mark around...
Calling all Grant experts please!
Just moved to a house with a Grant Vortex Condensing Combi 26 (2006) with full underfloor heating.
The plot so far:
All was happy until cranking the heating up to 27 degrees, next day no hot water.
Figured out if the heating was calling for heat the hot water...