2 new elements timer and temp pump but still not working properly,help

I have a pulsacoil 2000 and have had many problems this last week.First of all the the main trip went through the night then when re set the timmer was on constant.then latter tripped.so got a new ecomeny 7 timer but plumer said it was the bottom element again as I had one replaced last year.so I then had both elements replaced,the bottom one had blown and the top one was scaled.after this it still didn't work,called plumber back and said it could be the pump checked it and said it was running @ 41 and needed to be above 50.he has now put on a temp flowmaster pump.i do now get hot water but only when I put the boost on,the main one only worked once now doesn't fire up.there was one loose wire not connected but im sure that this was done when barrett homes sent gled hill to check boilers about 6 years ago.the plumber has reconnected this as he did try it unconnected but said he thinks it needs to be connected.so im now waiting for a new pump,but im not sure if that's the issue if the temp one has not complety solved the issue.please could I have some advice?

All the information you require can be found in the PC 2000 posts.
I can not really make that much sense of your post.
But here is a crash course.
There variations with the PC 2000 models, so it will be on the ones I work on.
You have a unit.
Top tank is used to fill the unit and vent any expansion.
Inside the unit you have 2 heaters.
Bottom one off peak
Top one on peak.
Both heaters have rod stats which should be set quite high. Check your book.
On top of the unit there is 2 pipes. If the fat pipe is hot and I mean hot then the unit is hot.
I presume it is full of water?
You have a pump.
A temperature sensor
A pump sensor
A pump drive PCB
Check the flashing light on the PCB and ref with the book.
If all is ok.
And the unit is hot.
Turn a hot tap on.
The sensors should tell the PCB what to do.
The pump should run.
Has the pump been bled of air?
Check the pump is running by removing big chrome screw on the front. Put finger tip in gently and feel if it is spinning.
You can stop it with your finger.
Running you should get hot water.
If not running is the PCB asking / telling the pump to run.
If it is there will be power to the pump. If there is power then it points to the pump.
Which needs to be the correct one!
If the unit is hot and the pump runs is the flow rate ok?
Could be the plate heat exchanger scaled up.
If unsure and the unit is hot.
Then you can put a temporary supply onto the pump. Get it running turn on the tap see what happens.
Test only not a fix!
There is also a single check valve located in a brass housing on one of the pump valves, they can play up although rare.
It needs to be in though never remove and leave out.
Your unit if old may have a reset trip located in side the unit ( see book)
Not really much else.
In my opinion you need the genuine Gledhill parts.
Ordinary heaters will not do at all.
Anything else you need to know you will find in the PC 2000 posts on here.
I will not write this again as it can now be used by many if they look and read these posts.
Mike

Hi not to take anything away, from what Mike is saying.

The pump needs to be a 15-60x18 Grundfos, Modulating pump, but would doubt the pump has failed.
The immersions need to be a long life superloy or incoloy far superior,
Going over your post, I would ask your plumber to do more research into your problem he needs to identify, where the current/energy is in the system.

Hi James, I think you hit the wrong button on your keyboard, the pump should be a Grundfos 15-50X18 Type: UPS modulating pump mate.