What do you do with the old hot water tap when connecting a cold fill washing machine?
This used to be a straightforward issue but unfortunately it’s been complicated by new information regarding a possible health hazard. The advice has always been to simply cap off the old hot water tap by screwing a special blanking cap onto it (details below). This would seal off the old tap and prevent accidental activation or leaks.
However, this advice is now seriously brought into question due to concerns about the dead-legs in plumbing that this practice creates (thanks to a comment from Colin Lewis). Basically, when any branch of plumbing goes to a dead end and water never flows through it again, the water trapped inside becomes stagnant and never gets replaced. If temperatures allow, bacteria and other micro-organisms can start growing in there creating a serious health risk. According to Mark Dowdeswell from Upnor.com this can create contamination of the rest of the water supply if some of it breaks away and joins the rest of the flowing water.
“A stagnation in a pipe line leads to massive grow of biofilm. Even a short dead leg can contaminate a whole system. Thermal and chemical disinfection will not solve the problem because it will never reach the dead leg due as there is no water flow.”
What are the possible health hazards?
If this was the cold water tap we were talking about there would be concerns about people drinking the water. The hot water doesn’t get drunk but it is possible some people may clean their teeth in hot water (I tried it myself a few times). The main issue with the hot water supply is much more serious because hot water may be used in power or mixer showers and the deadly Legionaries disease is notorious for being spread by airborne droplets if breathed in.
How real is this issue?
This is completely new to me, and not the remit of a repair engineer. However, I’ve spent several hours researching, and there are many credible sources (including government web sites) that warn against redundant pipework, and link it with Legionaries disease. That said, is this really a real and present danger requiring millions of homes to employ plumbers to remove all the old washing machine hot water pipework as soon as possible? It’s hard to believe, and I suspect the risk may be small – I’ve certainly not heard of any health cases and dead legs are clearly very common – but it is definitely a real issue.
All of the information I have found so far (including the quotes below) is advice aimed at people in charge of buildings (including landlords), employers and councils etc. I’ve found no advice aimed at informing us the general public. As yet there seems to be no recognition of the fact that over the last 10 years or so, millions of homes have newly created and often long runs of dead leg pipework since almost every washing machine stopped using hot water. The overwhelming majority of UK homes now have dead leg pipework running to their washing machines.
These quotes below from the UK government’s Health & Safety Executive web site regarding Legionnaires’ disease generally summarise the situation The control of legionella bacteria in hot and cold water
systems (PDF document)
2.77: Consideration should be given to removing infrequently used showers and taps and where removed, the redundant supply pipework should be cut back, as close as possible, to a common supply, eg to the recirculating pipework or the pipework supplying a more frequently used upstream fitting.
2.78: The risk from legionella growing in peripheral parts of the domestic water system, such as dead legs off the recirculating hot water system, may be minimised by regular use of these outlets. When outlets are not in regular use, weekly flushing of these devices for several minutes can significantly reduce the risk of legionella proliferation in the system. Once started, this procedure has to be sustained and logged, as lapses can result in a critical increase in legionella at the outlet. Where there are high-risk populations, eg healthcare and care homes, more frequent flushing may be required as indicated by the risk assessment.
So ideally remove all unused pipework
An article on this site here 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’ve no idea how likely or rare this is but for now it is wise to be aware of the potential issue, and best practice should be to have any redundant pipework removed altogether and capped off. This unfortunately means most people will need a plumber and have an unwanted expense so it is quite likely that most people will never bother to do it unless there is a highly respected source (such as government or Which?) warning about it. I suspect many plumbers are unaware of it even.
Another issue likely to cause reluctance 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’s not difficult to imagine a reversal of this practice, and a return of the hot water valve on future washing machines. I have personally pointed out several good reasons for reintroducing the hot water valve in my article on cold fill washing machines. It would be annoying to have all the pipework removed only to find your next washing machine uses hot water again but but having said that, health and safety is always an overriding concern.
Flushing the pipework
Current advice says that any existing dead leg pipework should be flushed at least every 7 days to remove any growth of bacteria and other micro-organisms. This would involve leaving the hot water hose connected to the hot tap and every 7 days placing it into a bucket and running the tap until piping hot water flushed through. This is clearly a highly unsatisfactory situation and unlikely to be taken up and carried out religiously by anyone but it is technically a potential solution.
All the facts that I currently know are here. I’ve also found an article that claims copper pipework restricts and suppresses the growth of biofilm but it doesn’t say it completely removes it – Legionella & Copper Plumbing. Information also says the legionella bacteria can’t survive above 60 °. But how can we be sure that our hot water is actually 60 ° and even if it is, much of it in the lower section of hot water cisterns and all over the pipe network spends long periods below 60 °. I am still researching this issue, if you have any expert opinion or any thoughts please add a comment or contact me and keep watching this article for updates.
The information below is from my original article regarding simply blanking off the old tap, which is no longer the best advice but in case you want to buy a blanking cap here it is –
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). You could also try searching Google for “3/4″ Brass blanking cap and washer” or specifically ask for that at DIY stores or plumbing merchants. The rubber 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.
- As a Landlord what are my duties? (Do you rent a house out?)
- Managing legionella in hot and cold water systems (QUOTE: “Legionella bacteria is commonly found in water. The bacteria multiply where temperatures are between 20-45°C and nutrients are available. The bacteria are dormant below 20°C and do not survive above 60°C.”)