Yet another no hot water problem on the Pulsacoil..........am I missing something?

Morning,

Could someone please shed some light on this Pulsacoil before it starts affecting my home life....

Initial callout - No hot water, lights pointing to sensors and/or PCB - Changed sensors & installed new PCB; GT147, GT153 & GT152
Still only roughly 3 minutes of luke warm water - Previous engineer changed the pump to one he must have had on van stock - Pump changed to modulating type; XB004
Still only roughly 3 minutes of luke warm water - Electrician checked all electrics timer, immersions etc. - all working.
Still only roughly 3 minutes of luke warm water - Drained system & checked for scale build up on immersions, bottom of cylinder & heat exchanger, all fine (heat exchanger flushed whilst out)

Still the problem persists, on all occasions we have spoken to Gledhill before carrying out and repairs and done as they advised.

Doubt it will make any difference but the system is run on standard electricity.

Has anyone got any ideas on what to do next as I'm at the end of my tether with it now.

Thanks.

Is the unit hot?
22 mm pipe on top of the units needs to be really hot.
Are the stats ok?
Timer / clock?
Store sensor?
If the unit is really hot.
And you have changed the pump drive PCB
DHW sensor
PHE sensor
And the pump.
Check all your connections carefully.
Next would be remove pump and on the bottom pump valve you have a single check valve fitted in a brass housing.
I have had one of these stick before after trying it about 10 times it stuck. Long shot.
Check the Y type in-line strainer too on the cold supply to PHE. There is a restrictor in there again a long shot.
Bled the DHW pump?
Did you descale the PHE ?
Mike