Small cottage, single story, vented direct hot water system and wood stove
with back boiler.

Friend reports that prior to this week

Bathroom wash hand basin hot tap was working well, kitchen hot tap OK, but
bath hot tap tended to "Air Lock" so bath not used for three years as
Electric Shower available and after the bath taps were used it needed the
owner to connect the wash hand basin taps together with a hose to get any
hot taps working again.

Back boiler in stove springs leak it is carbon steel and connected to the
120 litre direct, vented hot water tank. I volunteered to replace boiler
that was Thursday morning.

Boiler replaced in stove. Water turned on. Hot tank fills no problem. Goes
up to loft to see how storage tank is getting on. Finds it is 30 year old,
galvanised and is very rusty. I'm not happy but it fills up.

Without heating the hot water, tests tap. Very very low flow. Connects
washing machine pipes together as advised here. Puts thumb on vent pipe
after letting it flow for a while and water starts to come up outlet of
storage tank. So assume no large blockages.

One thing after then turning of the washing machine link and waiting a few
moments there is the sound of what appear to be air in the system moving
about!!

Now test hot water taps again. Wash hand basin about Ok but not as good as
before boiler replacement! Kitchen tap not wonderful but it is a mixer tap
and may not be suitable for a gravity system. Bath tap flow very poor. So go
into loft and the bath tap appears to start by draining the overflow pipe
and it appears there is not enough water rising from the hot tank below to
keep it running.

Cold storage tank in loft with it's outlet some 600mm above the level of the
loft floor. The outlet pipe drops to the loft floor, runs two metres
horizontal and then drops through ceiling, then 1.5 metres drop to the
bottom of the hot water tank. There are two pipe bends and a stop valve and
two tees in the run one for the boiler and a final one for a drain. Remove
stop valve it is opening fully with a small amount of gunge. Clean and
replace in system

From the top of the hot water tank the pipe work goes horizontal say 400mm,
90 elbow and rises say 500mm then through ceiling. ( That 90 elbow between
the horizontal and vertical pipe had gunge in it now cleaned but I'm scared
to remove top connection from cylinder as I may rip the top of the tank it
is ten years old.), then runs some 10 metres horizontal. then down through
ceiling two metres to the bath. On the way it goes through 3 off 90 elbows,
two 90 bends, a tee for the overflow and then gets to the bath. All these
pipes are 22mm.

Can anyone advise if this run is just too long and complicated for a gravity
system to run properly. I realise that a nasty old storage tank and steel
boiler are not helping either.

I have just ordered a few plastic storage tanks as the loft opening is tiny
and the storage tank needs replacing.