PRD problem with Triton Amber III Shower

[BigAl2]

In 2014 I bought a flat with a Triton Amber III Shower fitted over the bath. The long-standing tenant moved out recently, and I fitted a new shower hose and a new genuine Triton shower head with a multi-spray facility. Unfortunately, when I turned on the shower, water came out of the bottom of the unit.
I established that the cream-bodied PRD had blown, so fitted a new black one bought from Shower Doctor. I went through the commissioning procedure to the letter (but no debris came out at all) turning the lower dial backwards and forwards several times as detailed in the instructions.
When I turned the power on and tried the shower, some water came through the new hose and head, but I soon realised that water was also coming out of the bottom of the unit again.
Can anyone tell me why this should be happening? What are the possible faults which can cause the prd to burst?
If I have to replace the unit, which showers would be suitable and which ones would have the cable and pipe entries in the same place, to make the replacement an easy job?

 

[terryplumb]

Are you sure you carried out the commissioning procedure correctly ?
You should have connected the hose ,but not the shower head ,and ran water through with the temperature dial turned fully clockwise until all air was purged out and a constant stream of water comes through. You then slowly rotate the temperature dial ,with water still running ,anti clockwise /clockwise back and forth a few times. The above is done with heating elements OFF.

 

[BigAl2]

Yes, as I said, I followed the commissioning instructions to the letter (from the pdf sheet from Triton), including rotating the temperature dial, with water still running, from minimum to maximum several times to release any trapped air within the unit. There was a constant stream of cold water coming out, and no debris at all.
I then turned the power selector to the "STOP" position, connected the new shower head, and restarted the shower.

 

[terryplumb]

If the prv acted only when you fitted the shower head ,is the shower head the correct one for your shower model ?
The PRV re acts to back pressure build up ,so if the flow of water through the shower is restricted the built up pressure causes it to " pop". If the shower head is correct for your model ,then the shower internally is at fault.if its several years old I would fit a new shower. There are some models on the market ,such as a Triton easi fit ,which are designed for retro fitting ,and have adjustable water and supply cable connection points.

 

[BigAl2]

Many thanks for your help Terry.
Triton have told me that any Triton head will be suitable (the original also had a multi spray pattern facility),but that as the flat is in a hard water area, the heating element is likely to be furred up after at least six or seven years use.
They also think I should fit a new shower, so I am off to Screwfix now, to buy a Triton Enrich 8.5Kw shower for £49.99, which Triton told me is the same as their Triton Cara for £61.94, but with a slightly different front panel. Both have exactly the same connection positions for cable and pipework as the Amber III, so should be a fairly straightforward replacement.
Thanks again.