Hot Water Issue (frustrating)

[Al_74]

Hi I hope someone can help, I have an ongoing issue with the water in the bathroom. The bath and sink were pumping out luke warm water around 37-38 degrees on their own but the shower was stone cold. If I ran the shower and the bath or shower and sink together I would get piping hot water from the bath or sink but the shower never improved. I had a plumber out and he advised it was the diverter valve in my greenstar 28i combi boiler so he changed that to no avail. Next he stripped and cleaned the heat exchanger still no change followed by changing the sensor. Getting slightly desperate he then changed the PC board this still didn't change the problem and he never returned. I noticed the blue light never came on after he replaced the board so had a look to find he had not completely connected all the wiring I finished his job and restarted the boiler. I had hot water for the 1st time in ages but it only lasted until I tried to have a shower. I had hot water for baths and the sink had hot water but the shower remained cold. I have been ok with this for a while but today I tried the shower as I have people coming to stay and need the shower working again and now I am back to square one. No hot water in the bathroom unless I run the shower and bath at the same time, any help would be very grateful as I am a bit wary of calling another plumber after the last one.

[HowardKennitby]

How old is the system? How long have you had this problem?

Note of caution - if a 'plumber' starts swapping bits and nothing improves get rid. He/she obviously knows nothing.
Can you ask around for a recommendation from anyone else.

[Al_74]

Hi the boiler is 5 years old and the problem is now 2 - 3 months old. The worst thing is the plumber was recommended...

[ladybirder]

Have you spoken to the makers of the shower? Or looked up your model on line and checked the instruction manual if you haven't got one at home?
Regarding a plumber, we have "check-a-trade.com" in Sussex where people have recommended trades people. Do you have anything like that in your area?
I hope The Builder is looking in he will probably be able to help you.

[HowardKennitby]

I am not familiar with the workings of combi boilers so will have to bow out. Perhaps The Builder will notice this thread and respond.

[The Builder]

Al, my first thought is that none of the symptoms suggest a boiler problem. I guess the shower is a thermostatic valve. This shouldn't happen even with a manual valve, but thermo valves have a cartridge that can become faulty.
Can you give us the make and model?

The other thing that comes to mind is the layout of the pipework runs. It's a combi, so there'll be 15mm pipework for all the hot outlets, but even with mains pressure hot water, there could be "dead loops" in the layout.
This is unusual, but perhaps someone has altered the layout at some time, and not taken the best routes?

Has the pipework been altered in recent years?