In many applications you can use gate valves or ball valves, most plumbers I know prefer ball valves as these are less prone to freezing up due to corrosion if used infrequently.

I've never investigated a British domestic water supply system but am amazed it would incorporate an open top tank! Surely there would be a cover to keep unwanted things out, and where would the tank be located and how big would it be?

Does this replacement heater have a sealed burner? I've had a few water heaters go out in the past few years, one only 5 years old, and it seems that the newer sealed burner units don't last as long as the old fashioned kind. The last one to go would work once it was lit but the pilot would go out when the burner turned off. After endless messing around I gave up and junked it. From what I can see all manufactuers now use these sealed units.

I think it might have more to do with emissions as all the new water heaters have to be low NOx. I haven't noticed any difference in performance, but the sealed units surely seem less reliable over the long run. They are replaceable, but the cost for the burner unit is so high that it makes more sense to just buy a new heater.

Thanks for the explanation. I'm assuming the tank isn't too large, probably 30-60 gallons for an average home, and has some kind of a float valve to keep it filled plus an overflow just in case. What happens if a house has no attic space, how is this handled?

I do realize that this thread is from a year and a half ago, but some of us are a little late.  Boy, do I appreciate beekeyknee taking the time and effort to open our eyes on this subject.  Thanks Brian, yet again, and I hope that getting this thread back on the front page will help some other member to get onboard with the water heater problems.

After reading the thread, I immediately ordered a few new anode rods from Bradford White, for my own water heater, which was installed in Fall of 2007.

For those new to the issue, this is what they look like.  This is a Magnesium rod identical to that which came with the water heater when new.  Only a foot or so is visible in the photo, but the rod is just under 43 inches long and roughly 3/4 inch diameter.

So, after I received the new rods, I was naturally anxious to see what the original looked like after six and a half years.  And Brother, this is all that remains!  I did use a long magnet to search around inside the tank - but nothing was found there.

I should point out that here in Nevada we all use water softeners and that always eats up the anodes more quickly.  At least twice as quickly I am told.  Anyway, one look at this sad image makes it obvious that I have arrived far too late.  The water heater is still going along OK with heating the water, and no leaks so far.  But this image tells a bad, sad story of my failure to maintain the unit.

Another weakness I now realize we all need to be concerned with is the silt buildup inside the WH as time goes by.  I have drawn off a gallon or so of water every six months or so, and watched for silt in the bucket.  Now I know, that what is really needed is a full power, wide open flow of water out the drain in an effort to get as much of it as possible out of there.  From here on out I shall do that - wide open for five minutes, say.

Still another concern is how much opening we have for the water to flow out.  So, just to check it I pulled off the original drain tap to have a look.

And what I found certainly did surprise me.  This nasty looking mess is the inlet side of the tap.  Really clogged up with silt, crud and corrosion.

And look at the output end!  That is less than half open.   Not much way to get the kind of flow we need through a tap such as this one has become.

So we will be switching to another style.

This should help, at least somewhat, with getting the silt out.  The ball style valve is a straight route out, and a so called full-flow design.  That T fitting and extra pipe is the recirculating pump return, and has been there all along.

I may well have gotten with the program too late to save this water heater.  Will keep it going as long as possible though and use the experience to prepare for maintenance of the next one.

Put me down as a true believer, and thanks again to Brian for opening my eyes.