I'm not sure what Y strainer you are talking about. It appears you may have a filter fitted on the return heating pipe to the boiler (the 22mm right hand pipe).
There is a filter within the boiler. Is is located inside the lower connection on the pump. You have to remove the plastic elbow leading from the rear frame to the pump. Place a large tray under the boiler..if the filter's partially blocked when you remove it ( with a small screwdriver) you may get a few litres of water.
As for the DHW - unless your plumber can measure the burner pressures to further diagnose the fault it does appear the plate heat exchanger may be blocked. You need a Torx screwdriver to remove it. I think the 4 seals are also non standard so get these beforehand. If it's anything like the 80e model the plate's a complete bast**d to get out. The expansion vessel required serious levering to make some clearance.
There is a filter within the boiler. Is is located inside the lower connection on the pump. You have to remove the plastic elbow leading from the rear frame to the pump. Place a large tray under the boiler..if the filter's partially blocked when you remove it ( with a small screwdriver) you may get a few litres of water.
As for the DHW - unless your plumber can measure the burner pressures to further diagnose the fault it does appear the plate heat exchanger may be blocked. You need a Torx screwdriver to remove it. I think the 4 seals are also non standard so get these beforehand. If it's anything like the 80e model the plate's a complete bast**d to get out. The expansion vessel required serious levering to make some clearance.