Help who do I ask ?

while renovating a 400 year old property, I opted for a combi and underfloor heating. Builders son ( who said he was experienced) did this. Ive since learned its not been fitted well, and ive had many probs.(hes since disappeared)had lots of plumbers, but they havent a clue.I think its all about pressure etc, where can i get a plumber that knows, without paying a fortune? there doesnt seem to be any around locally. It seems the water is hot, but not going through the system. Now my domestic water is running hot.. but turning to cold. He didnt fit any zone thermostats at all.. ok.. I now realise , i did wrong giving him the job ! but how can i make a bad job good ? He didnt even leave details of the system