Glow worm Compact 100e Dhw prob

Hi Guys,
Daughters house........
Brief history..........
Probs since purchase with boiler Glow worm compact 100e............Boiler lockout taking place but reset after approx 4th attempt whether C/H or DHW called! Diff/Pr/Sw spindle not coming out much to make switch observed. Test to Differential Pressure Switch ( overiding) removed lock out situation but Dhw no real change. After 4th reset daily system operating o.k but Dhw never really given out much heated water. Luke warm, warm then cold variations and never lived upto filling a bath ( impossible)....
Kitchen refurb now taking place now.

Actions taken....

Drain down to system done, Diff/Pres/Switch and Dhw Switch Diaphrams replaced. Dhw switch Diaphram housing replaced also as found leaking and gunked at spindle. Pump head and gauge filter cleaned. Reassembled and refilled etc.

Situation now....
Boiler fires up lovely for Ch or Dhw.........but Dhw still as before, i.e luke warm and bath no chance at all.........
Central heating fantastic all around.
When C/H is on and operating now and Dhw called whilst it is on. The Dhw temp to taps is superb and lovely and hot. And a bath can be run and filled no problem, but only while C/H is operating!

Looking over the manual, I am thinking but can`t test until I am there that the Diverter switch/valve may have failed causing this problem. It would be great to sort it after it not working properly since her moving in ( 2 yrs).

Really would appreciate your experts thoughts on this or if you have had a similar problem and the fix with the Glow worm 100e on your travels?
Regards

Firstly establish a flow rate of about 10litres per min at the taps. If its too much more then it wont get very hot anyway.

Next with the CH cold, run a hot tap and feel if the CH flow pipe begins to warm. This would cause power to be lost to CH circuit and poor HW temp.

Next observe the burner does it stay lit constantly?

Assuming the burners constantly on, no power is being lost to CH and you have a flow rate of 10lpm< you need to do a gas rate. With the bath hot tap on and boiler fired ONLY (no cooker, fire etc) time the red dial on the front of your gas meter to do one revolution and post back results.

With this information (in seconds) we can determine how much the boiler is trying to heat the water

Thanks for reply. Will have to do over the next few days when at house. But will give feedback when tested.
Reading fault finder, removal of Diverter switch and manually pushing spindle in Diverter valve ( if it gives hot water on push in and C/h on release out would prove Diverter switch motor to be the fault? Will try that.
Regards

diverter valve motor/ pcb or needs new DV cartridge is my guess providing burner pressures are all correct and plate heat ex is clean...

Hi,
I am aware that no drain down is required to disconnect Diverter switch for test, but is a drain down required if removal of Diverter valve with pin in required?
Cheers!

Anyone changed the diverter valve with needle? Drain down required?
Cheers

yes, to change full diverter or to replace internals on it will require boiler to be drained