What do you do with the old hot water tap when connecting a cold fill washing machine?
The old hot water tap should be capped off by screwing a special blanking cap onto it (but first see update below). This is wise because I’ve heard of several cases where the unused hot tap has eventually started to drip, or even where the lever has been accidentally knocked partially on later. This can happen if the hot tap is in the kitchen sink cupboard. I’ve also seen cases where the washing machine itself moved about and knocked the lever when the hot tap was behind the washing machine. This isn’t so likely if your old hot water tap is a proper screw type but the ubiquitous red and blue lever taps are more prone to these issues and it’s safer to blank off any old unused washing machine tap, especially if they are installed out of sight.
Warning about buying blanking caps from DIY stores
I visited several major DIY stores including Wickes and B&Q trying to find a blanking cap for my old hot water tap. They only seemed to stock one blanking cap that looked anything like what I was after but after buying it and opening it, it was just fractionally the wrong size. Presumably it’s designed to cap off some other plumbing requirement. If I remember right I think it was 22 mm – I can’t recall, but I remember taking it over to an actual hot tap at Wickes and through the plastic packaging of both parts it did appear to be the right size. It wasn’t. The size you need if you want to try and source one from a shop is – 3/4″ Brass blanking cap and washer (which is around 19 mm).
Recommended source to buy blanking cap: It took me several wasted visits to large DIY stores, one wasted purchase (of one that was the wrong size) and a lot of time searching the Internet to find this product and I found a good source and linked to it. Sadly it appears they have closed down now, so the best I can recommend is that you search Google for “3/4″ Brass blanking cap and washer” or specifically ask for that at DIY stores or plumbing merchants. The seal is needed for proper sealing off of the old tap but if you don’t get one, try using one from the old hot fill hose.
Important update: Dead leg in plumbing
This article has just received a small comment from Collin Lewis asking – “Doesn’t blanking off the hot water pipe at the valve create a “dead leg” allowing bacteria to develop?“
I had never heard of this but within seconds I could work out exactly what he was referring to and so I spent some time researching the issue. When a length of pipework is capped off so that no water flows through it any longer all of the water inside the pipe becomes trapped. Because the tap is never turned on, this water stays trapped for ever and can apparently develop bacteria inside, which could in theory drift into the rest of the pipework.
I found this site which starkly states that dead legs in pipework are a major cause of Legionnaires’ disease UK urged to follow Europe and tackle ‘dead leg’ plumbing. I am still researching the issue in an attempt to work out how serious this actually is. Is it a theoretical threat? Does it only affect other countries i.e. hotter ones? Is it only a concern on cold water pipework, which we drink? All of these questions I hope to find the answers to shortly and will update this article accordingly. For now it is wise to be aware of the potential issue and best practice should be to have any redundant pipework removed altogether. This unfortunately means most people will need a plumber.
Another potential issue is that you might not want to have the pipework removed in case it is ever needed again in the future. This may be unlikely being as virtually all washing machines are cold fill only and have no hot water valve. However, it is not impossible to imagine a reversal of this practice and a return of the hot water valve on washing machines. I have personally pointed out several good reasons for reintroducing the hot water valve in my article on cold fill washing machines but having said that, health and safety is always an overriding concern. Keep an eye on this article for further updates.