Grohe Dump Valve

A few years ago I installed a new bathroom, and replaced the WC cistern with a concealed one. Not long after it was installed it started leaking water into the pan. It definitely wasn’t the overflow, and it was not too bad, so I left it to leak. It kept getting worse.

Now I remember some years ago hearing a debate about cisterns in this country and new EU regulations to free up the market. It used to be the case that a cistern had to have a siphonic valve to be legal in the UK. These are leak-proof by design. As soon as the cistern is empty, the siphon is lost and the water is trapped until the flush is operated again. The EU wanted the UK to drop the requirement for a siphonic flush because we were the only country in the world that manufactured them. Our rules were preventing import of cisterns from other EU countries, forming a trade barrier. Our bathroom manufacturers at the time claimed that other types of valve were not leak-proof, and therefore relaxing the regulation would cause a flood of wasted water to leak down our toilet pans. The EU won – and at the time I thought they were right – this was just protectionism masquerading as environmental concern. However, I have now been proved wrong. Non-siphonic cistern valves can and will leak, and when they do they are a pain to put right.

Eventually my cistern was leaking so badly that I had to do something about it. First of all I descaled it – we have extremely hard water and there was lots of lime scale in the cistern. That helped a bit, but after a few months it was leaking more than ever, and keeping us awake with its trickling noise. I took out the guts of the valve and took it to the local plumbers’ merchant to see if he could advise. “That’s a Grohe dump valve” he said; “if I could get hold of them I’d make a fortune.” Apparently these things are notorious, particularly in hard water areas. So over to Google to find out something about the Grohe dump valve and how you service them. I came across an interesting piece at How to mend it .com where someone had noticed a water bubble forming under the skin of the silicon washer. They said if you prick it with a pin you can remove the bubble, and allow the valve to seat properly. On inspection I found exactly such a bubble in both the washers in my valve. I pricked them with a pin, a tiny amount of water squirted out, and I was back in business. The thing now seals like new. Considering I had been contemplating replacing the cistern at a cost of at least £50, I think I’ve got off lightly. I wonder how long its’ going to last.

Update - see the epilogue