Can anybody help here-We run a wood burning stove with a back boiler
for hot water. After being on for half an hour we get a loud knocking
and have to turn it down. Is this air in the back boiler- and how does
it stay their- cold feed at bottom/hot at top. Can I cure this-
chemicals added to feeder tank? or some sort of air outlet value????
22mm pipe I think Any Advise appreciated.

On 17 Apr, 10:28, "
wrote:
Can anybody help here-We run a wood burning stove with a back boiler
for hot water. After being on for half an hour we get a loud knocking
and have to turn it down. Is this air in the back boiler- and how does
it stay their- cold feed at bottom/hot at top. Can I cure this-
chemicals added to feeder tank? or some sort of air outlet value????
22mm pipe I think Any Advise appreciated.

I sometimes get air trapped in my circulating pump which is at the top
(hot outlet) of my stove. This is because I put the pump in a
horizontal section of pipe and not vertical. I just bleed the air out
of the pump.
Does your knocking only occur with the pump off?
On a friends wood burning stove the fire itself would actually
oscillate/resonate very occasionally when it was first lit while
burning very dry kindling ferociuosly. The air shutters at the bottom
had to be shut off to stop this oscillation/resonance in the fire.
Try and see if the noise is in the fire/flue system or the water
system itself.
Is there any overflow back into the header tank?

Regards Chris.

On Thu, 17 Apr 2008 02:28:28 -0700 (PDT),
"
wrote:

Can anybody help here-We run a wood burning stove with a back boiler
for hot water. After being on for half an hour we get a loud knocking
and have to turn it down. Is this air in the back boiler- and how does
it stay their- cold feed at bottom/hot at top. Can I cure this-
chemicals added to feeder tank? or some sort of air outlet value????
22mm pipe I think Any Advise appreciated.

It sounds like you are boiling the water, which suggests the flow is
bad.

On Thu, 17 Apr 2008 17:56:40 +0100, EricP wrote:

Can anybody help here-We run a wood burning stove with a back boiler
for hot water. After being on for half an hour we get a loud knocking
and have to turn it down.

It sounds like you are boiling the water, which suggests the flow is
bad.

I'd agree. Maybe there is a pump in circuit that isn't being powered...

Solid fuel boilers really do need a free flowing gravity loop to the heat
sink (cylinder or radiator(s)) with no valves or pumps in the way. Not
only from the danger of the boiler literally boiling and possibly
rupturing but also with a pump when the power goes you have to damp down
or put out your independant source of heat and HW just when you want it!

--
Cheers
Dave.