Hi Brendan,
I had the Diaphram repaced a few months ago but that didnt fix the problem. Prochem replaced the two brass nuts at the front and said that should sort it. Cost me over a hundred quid and exactly the same happened on my very next job. theyve had the chemical pump apart and back together again so I think this is the last resort. I`ve been getting by by taking one of the pipes out of the chemical jug and just letting it leak outside the van but now its gone beyond that and I cant even turn the chemical gnob to the on position as it pours out. I have to spell gnob that way because if I spell it the proper way, the system turns the word to numpty!!!