I have an oil fired boiler system with two circuits, both pumped. One
drives the rads - which works fine, the other goes to the hot tank.
Since September I've had no hot water from the tank. I fitted a new
pump but no joy. What happens is this:

When the boiler has been running for a while the feed to the coil gets
hot as expected but no matter how long the boiler runs, all day even,
the return is always cold. If I switch off the pump I can hear the
water "falling" back down almost like the pump has been pushing
against a blockage.

So I drained the system and disconnected both ends of the coil and
there is standing water at both ends. I would have assumed that the
coil would have drained out via the bottom pipe when I emptied the
system, is this correct?

Does this all seem like the coil is blocked inside the tank. If so can
it be unblocked or is it time for a new tank.

House was built in 1995.

Ernie Bilko wrote:
I have an oil fired boiler system with two circuits, both pumped. One
drives the rads - which works fine, the other goes to the hot tank.
Since September I've had no hot water from the tank. I fitted a new
pump but no joy. What happens is this:

When the boiler has been running for a while the feed to the coil gets
hot as expected but no matter how long the boiler runs, all day even,
the return is always cold. If I switch off the pump I can hear the
water "falling" back down almost like the pump has been pushing
against a blockage.

So I drained the system and disconnected both ends of the coil and
there is standing water at both ends. I would have assumed that the
coil would have drained out via the bottom pipe when I emptied the
system, is this correct?

Does this all seem like the coil is blocked inside the tank. If so can
it be unblocked or is it time for a new tank.

House was built in 1995.



sounds blocked to me. Try blowing through it.

It may be scaled, in which case a flush with acid MIGHT get it sorted,
or destroy the heat exchanger..but it sounds too new for this to be an
issue.

On Sat, 06 Dec 2008 19:22:41 +0000, The Natural Philosopher
wrote:

Ernie Bilko wrote:
I have an oil fired boiler system with two circuits, both pumped. One
drives the rads - which works fine, the other goes to the hot tank.
Since September I've had no hot water from the tank. I fitted a new
pump but no joy. What happens is this:

When the boiler has been running for a while the feed to the coil gets
hot as expected but no matter how long the boiler runs, all day even,
the return is always cold. If I switch off the pump I can hear the
water "falling" back down almost like the pump has been pushing
against a blockage.

So I drained the system and disconnected both ends of the coil and
there is standing water at both ends. I would have assumed that the
coil would have drained out via the bottom pipe when I emptied the
system, is this correct?

Does this all seem like the coil is blocked inside the tank. If so can
it be unblocked or is it time for a new tank.

House was built in 1995.



sounds blocked to me. Try blowing through it.

It may be scaled, in which case a flush with acid MIGHT get it sorted,
or destroy the heat exchanger..but it sounds too new for this to be an
issue.


VERY soft water area. Never had so much as a hint of scale on anything
in the house.

"Ernie Bilko" wrote in message
...
I have an oil fired boiler system with two circuits, both pumped. One
drives the rads - which works fine, the other goes to the hot tank.
Since September I've had no hot water from the tank. I fitted a new
pump but no joy. What happens is this:

When the boiler has been running for a while the feed to the coil gets
hot as expected but no matter how long the boiler runs, all day even,
the return is always cold. If I switch off the pump I can hear the
water "falling" back down almost like the pump has been pushing
against a blockage.

So I drained the system and disconnected both ends of the coil and
there is standing water at both ends. I would have assumed that the
coil would have drained out via the bottom pipe when I emptied the
system, is this correct?

Does this all seem like the coil is blocked inside the tank. If so can
it be unblocked or is it time for a new tank.

House was built in 1995.

Have you noticed any automatic valves on the pipework? Some systems have a
zone valve, even if gravity fed or sealed, to close off the circulation to
particular parts of the loops. Have a look along the pipework for anything
that looks like a shiny metal, rectangular box which is fitted on the pipes.

If it does have closure valves, then the one for your hot water system might
be faulty and not opening to allow the water to flow through. The pump can
push as much as it likes, the valve won't budge. Which is what you are
describing.

Have another look and get back to us, please. Just to satisfy my curiosity.
:-)

"Ernie Bilko" wrote in message
...
I have an oil fired boiler system with two circuits, both pumped. One
drives the rads - which works fine, the other goes to the hot tank.
Since September I've had no hot water from the tank. I fitted a new
pump but no joy. What happens is this:

When the boiler has been running for a while the feed to the coil gets
hot as expected but no matter how long the boiler runs, all day even,
the return is always cold. If I switch off the pump I can hear the
water "falling" back down almost like the pump has been pushing
against a blockage.

So I drained the system and disconnected both ends of the coil and
there is standing water at both ends. I would have assumed that the
coil would have drained out via the bottom pipe when I emptied the
system, is this correct?

Does this all seem like the coil is blocked inside the tank. If so can
it be unblocked or is it time for a new tank.

House was built in 1995.

Blow through it. Does the pump have a check valve? It should as two pump
systems require one after each pump. Check that the valve is OK.

It will not be scale as it is on the primary side. It the system full of
sludge?

"Ernie Bilko" wrote in message
...
I have an oil fired boiler system with two circuits, both pumped. One
drives the rads - which works fine, the other goes to the hot tank.
Since September I've had no hot water from the tank. I fitted a new
pump but no joy. What happens is this:

When the boiler has been running for a while the feed to the coil gets
hot as expected but no matter how long the boiler runs, all day even,
the return is always cold. If I switch off the pump I can hear the
water "falling" back down almost like the pump has been pushing
against a blockage.

So I drained the system and disconnected both ends of the coil and
there is standing water at both ends. I would have assumed that the
coil would have drained out via the bottom pipe when I emptied the
system, is this correct?

Does this all seem like the coil is blocked inside the tank. If so can
it be unblocked or is it time for a new tank.

House was built in 1995.

It could be an air lock. The may be a bleed valve near the cylinder or you
may need to put one in.

Adam

On Sat, 06 Dec 2008 18:34:56 +0000, Ernie Bilko
wrote:

I have an oil fired boiler system with two circuits, both pumped. One
drives the rads - which works fine, the other goes to the hot tank.
Since September I've had no hot water from the tank. I fitted a new
pump but no joy. What happens is this:

When the boiler has been running for a while the feed to the coil gets
hot as expected but no matter how long the boiler runs, all day even,
the return is always cold. If I switch off the pump I can hear the
water "falling" back down almost like the pump has been pushing
against a blockage.

So I drained the system and disconnected both ends of the coil and
there is standing water at both ends. I would have assumed that the
coil would have drained out via the bottom pipe when I emptied the
system, is this correct?

Does this all seem like the coil is blocked inside the tank. If so can
it be unblocked or is it time for a new tank.

House was built in 1995.




Pump check valves are open. No motorised valve or anything else
between the pump and the coil. Very simple system, two loops two
pumps. Has worked perfectly for 13 years until now. When drained the
water looked pretty gunky. I was wondering if it is sludge and as the
system has been unused over the summer, it may have congealed and
blocked it. Top of the feed pipe is the expansion path to the F&E
cylinder so any air would go straing out. Also when I refilled I
filled from the system drain point using a hose so the system filled
from bottom to top. That should have shifted any trapped air.

Setting the pump speed to max has no effect either.

What concerned me most is that when I disconnected both ends of the
coil there was still water at the top coil connection on the tank,
i.e. the feed. If the coil was clear wouldn't the coil have drained
down with some water maybe at the bottom right angle joint, i.e. the
return.

Replacing the tank could be expensive as I have a Willis type
immersion heater, which is fantastic and I want to keep even if I need
a new tank.

"Ernie Bilko" wrote in message
...
On Sat, 06 Dec 2008 18:34:56 +0000, Ernie Bilko
wrote:

I have an oil fired boiler system with two circuits, both pumped. One
drives the rads - which works fine, the other goes to the hot tank.
Since September I've had no hot water from the tank. I fitted a new
pump but no joy. What happens is this:

When the boiler has been running for a while the feed to the coil gets
hot as expected but no matter how long the boiler runs, all day even,
the return is always cold. If I switch off the pump I can hear the
water "falling" back down almost like the pump has been pushing
against a blockage.

So I drained the system and disconnected both ends of the coil and
there is standing water at both ends. I would have assumed that the
coil would have drained out via the bottom pipe when I emptied the
system, is this correct?

Does this all seem like the coil is blocked inside the tank. If so can
it be unblocked or is it time for a new tank.

House was built in 1995.




Pump check valves are open. No motorised valve or anything else
between the pump and the coil. Very simple system, two loops two
pumps. Has worked perfectly for 13 years until now. When drained the
water looked pretty gunky. I was wondering if it is sludge and as the
system has been unused over the summer, it may have congealed and
blocked it. Top of the feed pipe is the expansion path to the F&E
cylinder so any air would go straing out. Also when I refilled I
filled from the system drain point using a hose so the system filled
from bottom to top. That should have shifted any trapped air.

Setting the pump speed to max has no effect either.

What concerned me most is that when I disconnected both ends of the
coil there was still water at the top coil connection on the tank,
i.e. the feed. If the coil was clear wouldn't the coil have drained
down with some water maybe at the bottom right angle joint, i.e. the
return.

Replacing the tank could be expensive as I have a Willis type
immersion heater, which is fantastic and I want to keep even if I need
a new tank.


The best way to find out exactly is to undo the coil and fish a drain spring
through it. If it's clear of any blockage the spring will pop straight
through. If it's blocked the spring should clear it out for you.

I do know, from my recent fluid dynamics learning (thanks Rod), that the
coil in the tank works like the bend in a river, and causes a fast and slow
running current as the water turns around the bends. The slow moving part
on the inside of the bend can deposit silt against the inside edge which is
not removed because the water is so slow moving. The silt build up over
time creates a narrowing in the pipe which only reinforces the slowing of
the water current even more, so more silt is deposited until the water is so
restricted that it blocks itself off.

You say you drained the system and found it really dirty, so it might be the
gunk that has built up in this part of the system, due to the effect
described. Push a drain spring through the coil to find out for sure. The
springs are cheap from the DIY sheds, and a fully re-usable for other
things.

It the only other thing I can think of.

"Ernie Bilko" wrote in message
...
On Sat, 06 Dec 2008 18:34:56 +0000, Ernie Bilko
wrote:

I have an oil fired boiler system with two circuits, both pumped. One
drives the rads - which works fine, the other goes to the hot tank.
Since September I've had no hot water from the tank. I fitted a new
pump but no joy. What happens is this:

When the boiler has been running for a while the feed to the coil gets
hot as expected but no matter how long the boiler runs, all day even,
the return is always cold. If I switch off the pump I can hear the
water "falling" back down almost like the pump has been pushing
against a blockage.

So I drained the system and disconnected both ends of the coil and
there is standing water at both ends. I would have assumed that the
coil would have drained out via the bottom pipe when I emptied the
system, is this correct?

Does this all seem like the coil is blocked inside the tank. If so can
it be unblocked or is it time for a new tank.

House was built in 1995.




Pump check valves are open. No motorised valve or anything else
between the pump and the coil. Very simple system, two loops two
pumps. Has worked perfectly for 13 years until now. When drained the
water looked pretty gunky. I was wondering if it is sludge and as the
system has been unused over the summer, it may have congealed and
blocked it. Top of the feed pipe is the expansion path to the F&E
cylinder so any air would go straing out. Also when I refilled I
filled from the system drain point using a hose so the system filled
from bottom to top. That should have shifted any trapped air.

Setting the pump speed to max has no effect either.

What concerned me most is that when I disconnected both ends of the
coil there was still water at the top coil connection on the tank,
i.e. the feed. If the coil was clear wouldn't the coil have drained
down with some water maybe at the bottom right angle joint, i.e. the
return.

Replacing the tank could be expensive as I have a Willis type
immersion heater, which is fantastic and I want to keep even if I need
a new tank.

Run a long wire through the coil, like a drain wire. Clear if necessary.
Replace check valves.
Insert a Meganclean filter on the boiler return, near to boiler.
Insert an in-line gauze filter on the same pipe near the filter.
Put in X-800 and stick to instructions.
Drain and flush and clean out F&E tank.
Fill and remove air.
Insert X-100 into Magnaclean filter.
Run for one day and clear filters.
Run for a week and clear filters.
Clear each week until clear.
Clean filters every year.
Pour in X-100 every 3.5 years. No need to drain.