Intermittent heating and water... Total frustration..

Hi
I really have tried to read around the topic but after four weeks of playing with radiators, checking temps, feeling pumps, taking readings I don't understand I just need help.
I have an ideal classic 18FE and BM2000. Past few months heating temp hasn't been best but past few weeks when thermostat has demanded a temp of 30 for CH the rads have been cold or warm. At times it comes on but it' seems this can be short term, and it soon goes off. With HW I can run a bath of piping hot water and once full it seems to be much lower, almost like the water has run out. When toppin up with HW it has even ran cold or lukewarm!!! If ever we use a cold tap when someone is in shower it's very noticeable even washing machine has an effect on HW pressure/ supply.... Can't run HW bath and have a shower... 5 bed house so this is often very necessary.
It's the sporadic heating that's the killer, I have operated the temp gauge inside the panel the LCD shows a variety of lines in various combinations and the word on. Sw2 readings have ranged from low 40s to high 50s HW 30-59, and the sw1 are 70/75 on both sw2 first two readings,,,, if that makes sense.
Had a variety of call outs and diagnostics paid for system cleanse with sentinel 800.... Plumber was very happy with the extracted water...... Ins send muppets ,,, had a suggestion but no diagnostics of dodgy thermostat it clicks but often does nothing?.....
Any advice I do have a good friend who loves this product and understands it but he lives 240 miles away and he has offered but I don't want a wasted trip or an expensive reunion...
I live north of Manchester and am fed up do spending my evenings trying to work it all out....

Check through the posts on here.
Also is the unit hot?
Is the heating pump working?
Water pressure low?
Can be PHE (plate heat exchanger) blocked up.
Also check the unit is full.
Mike

Second attempt at answering this...??? So apologies for the delay I thought I had done it...... Ok read lots and I struggle with the technical side of this.... The readings on SW1 & SW2?? Fault codes ect....??? I'm sorry.
The boiler mate isn't as hot as it used to be I use the room to dry clothes..... But it's not doing this so we'll.
The HPp is working but as I say intermittent the room stat is how I control heating and sometimes it works and house is hot and sometimes rads are lukewarm and stat is set to 30???
Pressure isn't much different .
Re the plate heater I had the system cleansed with sentinel last week, the plumber was more than happy with it he said it was clean and didn't see any reason for the problem to be sludge....????
Ref the unit being full the plumber would have done this???? The header tank is....
Sorry I'm not very helpful with the diagnostics, I have contacted my insurance and requested they send an engineer who is aware of this system..... I'm hoping he can help but I'm feeling it's pump related ????