HW pump

[dennis]

The industrial one. The small header tanks on most domestic systems would allow chlorinated water into the hot tank and keep it fairly clean. Then there is the 65C water that should be effective.

The lack of huge numbers of legionella outbreaks tends to indicate there is not a problem. When there is an outbreak its usually caused by spraying infected water around into the atmosphere where lots of people can breath it in.. not a typical household scenario. If you want to worry about something why not see if those pond misters that are about spread disease as they vapourise lots of potentially dirty water.

They did that because it was cheaper than being sued. Legion Ella can be caught from many places but if there is a source that can be identified you will get sued even if it came from elsewhere. A business needs to take that into account so procedures are there to minimise the risk of being sued (note I said sued not to minimise the risk of infection).

Lots of people have irrational fears.. don't panic, I am sure there is a self help group for you somewhere.

I think the risks are a lot lower than you think. Compare the number of infections and deaths to those cause by falls getting out of bed/dressing and you may get a clue.

[dennis]

You want an area of still water.. if you squirt the cold in it will mix with the hot and start lowering the temp as soon as you turn the tap on. As for stagnant water.. the water at the bottom will be replaced by the colder inlet water even in a flat bottomed tank.. cold water sinks. The only time it might not happen is if you are preheating the inlet with (say) solar.

[Doctor Drivel]

Nearly. Some do. Many run at 65-70C store temperature. A good plate heat exchanger will heat the cold mains to over 60C, then it is blended down. Gledhill modulate the DHW pump to maintain the DHW outlet temp. using stored water from 75 to 82C.

Limscale in potable water will not clog a large plate heat exchanger (well not quickly). The plates flex and prevent scale build up. Combi plate heat exchnager are small and the plates do not flex.

Sludge in thermal stores is another matter entirely. That is poor design of the store and poor installation. I have seen some well over 20 years old (with internal DHW coils) and still working brilliantly and not a sign of sludge. The biggest sludge buckets are rads. They collect the stuff in volume.

[Doctor Drivel]

Please eff off as you are a plantpot.

[Doctor Drivel]

Oh no!! Not the two wrongs make a right argument. Legionella is domestic systems is preventable.

A scenario. family goes on summer hols. house is left empty and in three weeks the temps inside the loft get to 55C at times. Perfect for legionella to breed in the cold tank in the loft. The family get back and it is very hot, so one takes a cold shower with infected cold water from the tank. If a mains pressure system then this scenario can't occur.

Not heating DHW above 60C can bring it on. This is where normal cylinders and unvented cylinders are not effective enough. Stored water combis are good in that the stored water is above 60C and when it runs out of stored hot water the combi reverts to what the boiler can give at a lower flowrate.

[Doctor Drivel]

A pipe stat can be fitted when the loop is up to temperature and it switches off the pump. IF a mains pressure loop the instant hot water can be used for kettles reducing the electricity bill, so offsetting the running cost of the pump. If on a water meter it also reduces water waste and again cost offset. Also instant hot water into a washing machine. Many just fill up the machine with cold water from the dead-leg DHW draw-off pipe and then the expensive to run electric element kicks in. And the great convenience of having instant hot water at taps. So,they are not financial dead loss.

Well worth doing as long as the loop is very well insulated and a pipe stat fitted.

[Appin]

The message from "Doctor Drivel" contains these words:

Must be an old washing machine. Almost all washing machines now are cold fill only -- as is generally true of dishwashers also.

[Dave Plowman (News)]

So something else you're just quoting without understanding. Figures.

[Dave Plowman (News)]

No need to go on summer holidays if they already live in the middle of the Sahara desert.

[Doctor Drivel]

The more economical machines are hot and cold fill to use cheaper gas heated water.

[Appin]

The message from "Doctor Drivel" contains these words:

I know the reasoning perfectly well. The question which new model designs are using h and c fill?

[Doctor Drivel]

Please eff off as you are a total plantpot.

[Doctor Drivel]

Please eff off as you are a plantpot.

[Rod]

I just checked on the John Lewis web site - a random selection of four washing machines (3 A+ and one A rating) - all cold fill only. Are any new washing machines hot & cold fill?

They (JL) say that cold fill is better because the hot water fill would normally be at too high a temperature so would require cooling down (for many programs).

That said, if they are available, hot and cold fill might be more economical for those who do a large proportion of hot washes for some reason.

[nightjar]

They can breed to dangerous levels in water once it gets above 25C, according to the WHO.

Colin Bignell

[nightjar]

More than 4500 cases of an avoidable diseaes across Europe in 2004 suggests it is enough of a problem to need to be addressed.

That certainly is how the cases that attract the media happen. They tend to find the general backgound of individual cases much less newsworthy. One form of Legionella infection has even been linked to the use of potting compost in Australia, the USA and Japan. The mechanism for that is particularly obscure.

WHO figures for France in 2002 (probably typical for Europe) show that 10% of cases were hospital acquired infection, compared to 12% linked to stays in hotels or camp sites. However, only 43% of cases could be linked to a specific risk cause, so between them, those represent about half of the identifiable causes.

....

There are at least 50 species and 70 distinct serogroups of Legionella - 16 serogroups in L pneumophilia. It is not that difficult to achieve a high level of confidence of match between an outbreak and the source.

Colin Bignell

[Doctor Drivel]

Decent machines do not allow hot in on settings below 60C, so that is crap.

I know most dishwashers are cold fill only, but some will allow hot fill and this means a hot rise too. It is more economical overall even though the rise is hot, that heating the water with electricity all the way. It is also quicker as the machine does not stand while the element heats the water.

In the USA most machine many w/machines have no internal heaters relying on the water temp from the house, so it makes the product cheaper. Makes sense.

[Dave Plowman (News)]

Most modern machines use so little water there won't be time for it to run hot. A machine which does use a lot of water - like most top loaders - are wasteful of both water and detergent.

[Dave Plowman (News)]

Top loaders usually are as they use a lot of water.

On the majority of installations the water wouldn't have time to run hot before the machine is full.

I doubt it's worth the hassle.

[Dave Plowman (News)]

Most US washers are top loaders wasting both water and detergent, weed.