Combi Boiler knocking
 

Hello all,

I've a Ikon-t gas combi boiler that's been installed for about four
years. Unfortunately it's developed a fault. When hot water is called
for, either by a hot tap or the heating is switched on, the boiler
hums then the gas lights up. All as normal.

However, after a few seconds the needle on the pressure gauge jerks
around as high as it can go and the boiler starts to make a knocking
sound. Then the safety cut-out light comes on. After that the needle
on the pressure dial slowly drops back to normal.

I've checked that the tap on the filling loop is closed.

What might it be?

Combi Boiler knocking
 

"Chade" wrote in message
...
Hello all,

I've a Ikon-t gas combi boiler that's been installed for about four
years. Unfortunately it's developed a fault. When hot water is called
for, either by a hot tap or the heating is switched on, the boiler
hums then the gas lights up. All as normal.

However, after a few seconds the needle on the pressure gauge jerks
around as high as it can go and the boiler starts to make a knocking
sound. Then the safety cut-out light comes on. After that the needle
on the pressure dial slowly drops back to normal.

I've checked that the tap on the filling loop is closed.

What might it be?

Where is the needle when the boiler is cold?

Combi Boiler knocking
 

On 3 Feb, 19:09, "John" wrote:
"Chade" wrote in message


What might it be?

Where is the needle when the boiler is cold?

Just over 1 Bar, which is in the normal range.

Combi Boiler knocking
 

On Feb 3, 8:02*pm, Chade wrote:
On 3 Feb, 19:09, "John" wrote:

"Chade" wrote in message

What might it be?

Where is the needle when the boiler is cold?

Just over 1 Bar, which is in the normal range.

Is it possible that the circulation pump has failed? The water is not
circulating through the heat exchanger. the water then boils making
the bumps and leaps in pressure that you see. the flow thermostat
takes a while to register because there is no flow. When it does it
turns off the heat.

Robert

Combi Boiler knocking
 

On 3 Feb, 20:07, RobertL wrote:
On Feb 3, 8:02 pm, Chade wrote:

On 3 Feb, 19:09, "John" wrote:

"Chade" wrote in message

What might it be?

Where is the needle when the boiler is cold?

Just over 1 Bar, which is in the normal range.

Is it possible that the circulation pump has failed? The water is not
circulating through the heat exchanger. the water then boils making
the bumps and leaps in pressure that you see. the flow thermostat
takes a while to register because there is no flow. When it does it
turns off the heat.

Makes sense. Is there anyway to confirm?

Combi Boiler knocking
 

"Chade" wrote in message
...
On 3 Feb, 20:07, RobertL wrote:
On Feb 3, 8:02 pm, Chade wrote:

On 3 Feb, 19:09, "John" wrote:

"Chade" wrote in message

What might it be?

Where is the needle when the boiler is cold?

Just over 1 Bar, which is in the normal range.

Is it possible that the circulation pump has failed? The water is not
circulating through the heat exchanger. the water then boils making
the bumps and leaps in pressure that you see. the flow thermostat
takes a while to register because there is no flow. When it does it
turns off the heat.

Makes sense. Is there anyway to confirm?

Flow and return pipe temperatures would indicate a flow or no flow I would
imagine.

Combi Boiler knocking
 

On 3 Feb, 20:39, Chade wrote:
On 3 Feb, 20:07, RobertL wrote:


Is it possible that the circulation pump has failed? The water is not
circulating through the heat exchanger. the water then boils making
the bumps and leaps in pressure that you see. the flow thermostat
takes a while to register because there is no flow. When it does it
turns off the heat.

Makes sense. Is there anyway to confirm?

Wait. It does it when the boiler is set to just hot water and the hot
tap is on. If it's just hot water and not heating, would a pump be
involved?

Combi Boiler knocking
 

On 3 Feb, 19:09, "John" wrote:
"Chade" wrote in message


I've checked that the tap on the filling loop is closed.

What might it be?

Where is the needle when the boiler is cold?

Although we've not been using it, obviously, the needle has now
dropped back to nearly zero.

Combi Boiler knocking
 

On 5 Feb, 02:43, John Rumm wrote:
Chade wrote:
On 3 Feb, 19:09, "John" wrote:
"Chade" wrote in message

I've checked that the tap on the filling loop is closed.
What might it be?
Where is the needle when the boiler is cold?

Although we've not been using it, obviously, the needle has now
dropped back to nearly zero.

Top it up to 1 bar again, and see what happens when you leave it for a
couple of hours (unused).


After a couple of hours it seems to be staying at 1 Bar.

Combi Boiler knocking
 

A big thank you to everyone who commented. Following the instructions
in the boiler's manual I managed to remove the water pump. I tried the
local plumbing place and they recommended Parts Center, who ordered a
replacement pump for me. A quick trip back to Part Center when I
noticed the new pump pumped the opposite way, but I was assured that
for that particular boiler the part had been 'enhanced'. So I fitted
the new pump, filled the system, crossed my fingers and switched on.
Wow, hot water and heating. :)

While I was there I overheard someone discussing adding chemical
additives to the radiator water to prolong boiler and radiator life.
Is there anything in this? It's not a hard water area, the kettle only
has a trace of limescale, plus there is an electronic water descaler
fitted to the water pipe near where it enters the house.

Combi Boiler knocking
 

On 5 Feb, 22:45, John Rumm wrote:
Chade wrote:
On 5 Feb, 02:43, John Rumm wrote:
Chade wrote:
On 3 Feb, 19:09, "John" wrote:
"Chade" wrote in message
I've checked that the tap on the filling loop is closed.
What might it be?
Where is the needle when the boiler is cold?
Although we've not been using it, obviously, the needle has now
dropped back to nearly zero.
Top it up to 1 bar again, and see what happens when you leave it for a
couple of hours (unused).

After a couple of hours it seems to be staying at 1 Bar.

If you fire it up and watch the pressure gauge, what does it do?

Rapidly increases by just under a third of a Bar then stops, falling
back to the starting pressure when the pump cuts out.

The pressure seems to have stabilised now, no-longer dropping over
time.

A rapid
rise to higher than normal (i.e. 3 bar) would indicate your expansion
chamber has lost its air charge. If you can find the charge valve for it
(it will look like a car type inflation valve (for that is indeed what
it is)), a quick press on the centre pin should yield a puff of air. No
air would indicate a discharged vessel in need of pumping up. Water
would indicate a ruptured diaphragm inside it, meaning it needs
replacing or, more likely, another one adding to the system elsewhere.
(allowing some air into a rad may function as expansion space for a
stopgap to get the heat back on)


Should I still do this test even though it seems to be working
normally?

Combi Boiler knocking
 

John Rumm wrote:
Chade wrote:
On 9 Feb, 22:15, John Rumm wrote:


A rapid
rise to higher than normal (i.e. 3 bar) would indicate your expansion
chamber has lost its air charge. If you can find the charge valve for it
(it will look like a car type inflation valve (for that is indeed what
it is)), a quick press on the centre pin should yield a puff of air. No
air would indicate a discharged vessel in need of pumping up. Water
would indicate a ruptured diaphragm inside it, meaning it needs
replacing or, more likely, another one adding to the system elsewhere.
(allowing some air into a rad may function as expansion space for a
stopgap to get the heat back on)

Should I still do this test even though it seems to be working
normally?

Not it its working ok.


The pressure dropped again by about a third of a bar overnight. After
consulting a diagram in the manual I removed the inner boiler cover
and found that the valve is gently weeping. What spare parts do I need?

Combi Boiler knocking
 

On 11 Feb, 15:32, John Rumm wrote:
Chade wrote:
John Rumm wrote:
Chade wrote:
On 9 Feb, 22:15, John Rumm wrote:

A rapid
rise to higher than normal (i.e. 3 bar) would indicate your expansion
chamber has lost its air charge. If you can find the charge valve for it
(it will look like a car type inflation valve (for that is indeed what
it is)), a quick press on the centre pin should yield a puff of air. No
air would indicate a discharged vessel in need of pumping up. Water
would indicate a ruptured diaphragm inside it, meaning it needs
replacing or, more likely, another one adding to the system elsewhere.
(allowing some air into a rad may function as expansion space for a
stopgap to get the heat back on)
Should I still do this test even though it seems to be working
normally?
Not it its working ok.

The pressure dropped again by about a third of a bar overnight. After
consulting a diagram in the manual I removed the inner boiler cover
and found that the valve is gently weeping. What spare parts do I need?

Which valve are we talking about...

There are two likely candidates: The expansion chamber valve and the
overpressure release valve. Since the overpressure release valve ought
to be piped outside in 15mm copper pipe, I expect that we are talking
about the former.


Sorry if I'm not being clear but I'm a bit confused. I just found the
expansion vessel in my boiler diagram and it has a 'car valve' on top
I depressed it and was greeted by a puff of air. There is a second
'car valve' in my boiler which is on top of what my diagram calls the
"Automatic air vent" that is the one that's weeping. Your first link
called it an "Bottle air vent".

http://www.bes.co.uk/products/109.asp

I could keep pressing the valve on top of the expansion vessel to see
if water comes out eventually but I'm nervious about letting out too
much air.