Problem with Grant Combi Boiler - no hot water

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16 Dec 2019
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Morning all,

I’m having a problem with my boiler I’m hoping you can help with.

I have a Grant Vortex 21e Combi Boiler (Oil). There was a leak (now sorted) which caused the electrics on the HW pump to burn out. I’ve replaced the pump however there is still no hot water.

When the hot tap is run the flow light comes on and the burner fires but after about 5 minutes the overheat cut off activates.

The pipe leading into the Heat Exchanger gets warm, but the exchanger itself is not getting hot. I have removed the heat exchanger and cleaned it out (I live in a hard water area) and I can get a good flow through it so I don’t think it’s blocked. I’ve also cleaned/descaled the TMV.

I’m now at a loss as to what it could be, prior to replacing the pump (which seems to be working fine) everything was ok – does anyone have any ideas?

Thanks in advance
 
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Have you fully vented the store and pump.
Is the pump running on full speed are pump valves open ?
 
Thanks for the reply - the pump is on full speed and the valves are open - could you explain what you mean by venting the store and pump please?
 
Are the caps on auto air vents open. There is a manual vent on flow pipe as well.
 
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Yes, all open and working. Have bled the manual one on the flow pipe.
 
Yes, when the tap runs the flow light comes on and the burner fires
 
Yes, all the lights are behaving as they should be. It just runs for five minutes without the heat exchanger getting even warm before the overheat cut off activates. Was wondering if it might be a thermistor?
 
Have you checked for 240v at pump terminals..
A faulty store thermistor would give a flashing light.
Is heating ok.
 
If the store is Hot the pump is running but no heat to the PHE then there is an air lock or blockage.

Is the pump correct way round ???

No flow if wrong due to NRV
 
Pump is the same way around as the old one, happy it's going the right way. If it's a blockage what's the best way of clearing it?

Thanks for the help!
 
Are you sure that the arrow on the pump BODY....not the head is pointing down. It seems strange the fault started after you swapped the pump.
Have you loosened the screw on pump head and checked it is rotating and there is no trapped air.
 
The head is pointing up, tbh I don't think you could get it to fit upside down just because of the shape of it. Have loosened the screw and got water out, I did check it was rotating before I put the water back on initially, seemed ok?
 

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