"echo21" wrote in message
...
Hi all,

I have noticed something weird (to me, pribably not to you!) about my hot
water and central heating system.

This is continuing from my last post (here it is again just in case...):

--I have a conventional vented central heating system with a Potterton
Prima
B
--boiler and a header tank in the loft.

--The boiler is very noisy when heating the hot water for the cylinder,
even
--when the boiler is not lit and only pumping - is this kettling?

--If so, will I need to flush and treat the system?

--I am OK to do this apart from one small problem - I cannot find the
drain
--tap on any rads!
--The only thing that looks like a drain tap is above the boiler on one of
the
--two pipes at the top labelled 'flow'

--The other pipe at the top, I am assuming, is the return - there is a
third
--pipe at the bottom of the boiler which is the same width as the pipes
going
--to the rads - what is that?

--If the tap on the flow pipe is the tap I need, how is it possible to get
all
--the sludge out of the rads which are lower than the boiler?

--Thanks in advance for any help you can offer.

I have since noticed that the noise is more of a whoshing noise with lots
of bubbling sounds - this noise does not occur when the heating is on -
the
heating has been off for a few weeks due to the ambient temp - since
realising this, I spoke to a friend who said that there system had similar
symptoms and had a faulty pump - could this be the problem? The pump is
only a year old.

--
Jim

If you get a bubbling, whooshing sound when the pump turns off then you may
have air trapped in the system. The pump is forcing it down the pipework
then when the pump goes off the air rises again. You sort this by bleeding
the pump - normally a plastic screw on the front which lets air and water
out when you unscrew it.

If you get the bubbling when the boiler is not firing but just after it has
stopped firing this suggests that the pump may have turned off with the
boiler and water is no longer flowing through the boiler so the remaining
heat from the firing boils the water. If so, you may have strange wiring on
the hot water side. Or may just have a set up like mine which gives very
minor 'kettling'.

What I think should happen is that the pump should run continuously while
your programmer has 'hot water' turned on, as long as the gate valve for the
heating coil is open. The boiler fires up then stops again depending on the
water temperature of the water being pumped through the boiler. Once the hot
water cylinder thermostat detects you are up to temperature, the gate valve
should close and cut power to the boiler. At this point some systems run the
pump for a little longer (through a bypass loop) to prevent this 'kettling'.
Others, like my old one, just turn the pump and boiler off and you can get a
bit of noise.

You won't notice this if the central heating is on because the pump is
always on pushing water round the radiators. You will only get this when you
are running hot water only.

HTH
Dave R