Hi to all,

My combi is on the blink. It's an Ariston Microgenus - the old model, it's not a condensing boiler.

Symptoms: shower oscillates between hot and cold. In fact so do any of the taps when opened. Aha! Clearly the secondary heat exchanger is clogged. I've had enough experience of that one in the past, and that's not the problem.. I've cleaned out the secondary heat exchanger - no better. So I replaced the secondary heat exchanger - no better!

So the question is, what else could cause this problem. It seems not to be a fault with the (theormostatic) shower, because the same happens when any tap(s) are opened, I've tried that one. Could it be the pump failing, and not getting heat away quickly enough? Or I guess the sensor thinking the DHW is hotter than it is, and shutting down the boiler when it doesn't need to shut down? Or the PCB (which seems to be the standard diagnosis when all else fails).

I could easily run up a bill of a couple of hundred in replacing parts that don't need replacing, so any guidance would be welcome before I start lining the pockets of the local plumbers' merchant. Good thing it's summer.

Cheers!

Martin

On Sat, 07 Jul 2012 15:54:35 +0100, Martin Pentreath wrote:

Hi to all,

My combi is on the blink. It's an Ariston Microgenus - the old model, it's not a condensing boiler.

Symptoms: shower oscillates between hot and cold. In fact so do any of the taps when opened. Aha! Clearly the secondary heat exchanger is clogged. I've had enough experience of that one in the past, and that's not the problem. I've cleaned out the secondary heat exchanger - no better. So I replaced the secondary heat exchanger - no better!

So the question is, what else could cause this problem. It seems not to be a fault with the (theormostatic) shower, because the same happens when any tap(s) are opened, I've tried that one. Could it be the pump failing, and not getting heat away quickly enough? Or I guess the sensor thinking the DHW is hotter than it is, and shutting down the boiler when it doesn't need to shut down? Or the PCB (which seems to be the standard diagnosis when all else fails).

I could easily run up a bill of a couple of hundred in replacing parts that don't need replacing, so any guidance would be welcome before I start lining the pockets of the local plumbers' merchant. Good thing it's summer.

Cheers!

Martin

On average your hot water is warm. Stop moaning.

--
http://petersparrots.com
http://petersphotos.com

How do you embarrass an archeologist?
Give him a used tampon and ask him which period it came from.

On Saturday, July 7, 2012 4:55:43 PM UTC+1, Lieutenant Scott wrote:
On Sat, 07 Jul 2012 15:54:35 +0100, Martin Pentreath wrote:

Hi to all,

My combi is on the blink. It's an Ariston Microgenus - the old model, it's not a condensing boiler.

Symptoms: shower oscillates between hot and cold. In fact so do any of the taps when opened. Aha! Clearly the secondary heat exchanger is clogged. I've had enough experience of that one in the past, and that's not the problem. I've cleaned out the secondary heat exchanger - no better. So I replaced the secondary heat exchanger - no better!

So the question is, what else could cause this problem. It seems not to be a fault with the (theormostatic) shower, because the same happens when any tap(s) are opened, I've tried that one. Could it be the pump failing, and not getting heat away quickly enough? Or I guess the sensor thinking the DHW is hotter than it is, and shutting down the boiler when it doesn't need to shut down? Or the PCB (which seems to be the standard diagnosis when all else fails).

I could easily run up a bill of a couple of hundred in replacing parts that don't need replacing, so any guidance would be welcome before I start lining the pockets of the local plumbers' merchant. Good thing it's summer.

Cheers!

Martin

On average your hot water is warm. Stop moaning.


Haha! On average my palm is halfway between my shoulder and your face, stop shouting.

On Sat, 07 Jul 2012 17:14:43 +0100, Martin Pentreath wrote:

On Saturday, July 7, 2012 4:55:43 PM UTC+1, Lieutenant Scott wrote:
On Sat, 07 Jul 2012 15:54:35 +0100, Martin Pentreath wrote:

Hi to all,

My combi is on the blink. It's an Ariston Microgenus - the old model, it's not a condensing boiler.

Symptoms: shower oscillates between hot and cold. In fact so do any of the taps when opened. Aha! Clearly the secondary heat exchanger is clogged. I've had enough experience of that one in the past, and that's not the problem. I've cleaned out the secondary heat exchanger - no better. So I replaced the secondary heat exchanger - no better!

So the question is, what else could cause this problem. It seems not to be a fault with the (theormostatic) shower, because the same happens when any tap(s) are opened, I've tried that one. Could it be the pump failing, and not getting heat away quickly enough? Or I guess the sensor thinking the DHW is hotter than it is, and shutting down the boiler when it doesn't need to shut down? Or the PCB (which seems to be the standard diagnosis when all else fails).

I could easily run up a bill of a couple of hundred in replacing parts that don't need replacing, so any guidance would be welcome before I start lining the pockets of the local plumbers' merchant. Good thing it's summer.

Cheers!

Martin

On average your hot water is warm. Stop moaning.

Haha! On average my palm is halfway between my shoulder and your face, stop shouting.

Insufficient information. What percentage is your arm extended? What is your reaction speed?

--
http://petersparrots.com
http://petersphotos.com

Excuse me, are you reading that paper you're sitting on?

On 07/07/2012 15:54, Martin Pentreath wrote:
Hi to all,

My combi is on the blink. It's an Ariston Microgenus - the old model, it's not a condensing boiler.

Symptoms: shower oscillates between hot and cold. In fact so do any of the taps when opened. Aha! Clearly the secondary heat exchanger is clogged. I've had enough experience of that one in the past, and that's not the problem. I've cleaned out the secondary heat exchanger - no better. So I replaced the secondary heat exchanger - no better!

So the question is, what else could cause this problem. It seems not to be a fault with the (theormostatic) shower, because the same happens when any tap(s) are opened, I've tried that one. Could it be the pump failing, and not getting heat away quickly enough? Or I guess the sensor thinking the DHW is hotter than it is, and shutting down the boiler when it doesn't need to shut down? Or the PCB (which seems to be the standard diagnosis when all else fails).

I could easily run up a bill of a couple of hundred in replacing parts that don't need replacing, so any guidance would be welcome before I start lining the pockets of the local plumbers' merchant. Good thing it's summer.

Cheers!

Martin

When you open a tap and get alternate hot and cold water, is the flow
rate constant - or is it slow when hot and fast when cold? Is the boiler
firing the whole time this is happening?

I don't claim to be an expert on combis - but answering these questions
may help someone who is to home in on flow sensors, diverter valves, or
whatever.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

Martin Pentreath wrote:

My combi is on the blink. It's an Ariston Microgenus - the old model, it's
not a condensing boiler.

Symptoms: shower oscillates between hot and cold. In fact so do any of the
taps when opened. Aha! Clearly the secondary heat exchanger is clogged.
I've had enough experience of that one in the past, and that's not the
problem. I've cleaned out the secondary heat exchanger - no better. So I
replaced the secondary heat exchanger - no better!

So the question is, what else could cause this problem.

Blocked main heat exchanger, slow running pump, faulty temperature
sensor on hot pipe/heat exchanger.

If the water from your radiators is pretty black, then the main heat
exchanger is probably blocked with this gunk.
Pump is a possibility, but for £80+, it is a bit expensive to change it
to find it is not that.
Temp. sensor - maybe not, if the water is set to a low temperature, at
the boiler, does it still cut out after a few minutes whe4n running the
hot water?
If so, main heat exchanger is the most probable cause.
Not worth changing it, it is new boiler time.

Alan.
--
To reply by e-mail, change the ' + ' to 'plus'.

On 07/07/2012 15:54, Martin Pentreath wrote:
Hi to all,

My combi is on the blink. It's an Ariston Microgenus - the old model,
it's not a condensing boiler.

Symptoms: shower oscillates between hot and cold. In fact so do any
of the taps when opened. Aha! Clearly the secondary heat exchanger is
clogged. I've had enough experience of that one in the past, and
that's not the problem. I've cleaned out the secondary heat exchanger
- no better. So I replaced the secondary heat exchanger - no better!

So the question is, what else could cause this problem. It seems not
to be a fault with the (theormostatic) shower, because the same
happens when any tap(s) are opened, I've tried that one. Could it be
the pump failing, and not getting heat away quickly enough? Or I
guess the sensor thinking the DHW is hotter than it is, and shutting
down the boiler when it doesn't need to shut down? Or the PCB (which
seems to be the standard diagnosis when all else fails).

I could easily run up a bill of a couple of hundred in replacing
parts that don't need replacing, so any guidance would be welcome
before I start lining the pockets of the local plumbers' merchant.
Good thing it's summer.

While I appreciate its not the best time of the year for this, can it
run the rads ok?



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Saturday, July 7, 2012 7:15:36 PM UTC+1, John Rumm wrote:
On 07/07/2012 15:54, Martin Pentreath wrote:
Hi to all,

My combi is on the blink. It's an Ariston Microgenus - the old model,
it's not a condensing boiler.

Symptoms: shower oscillates between hot and cold. In fact so do any
of the taps when opened. Aha! Clearly the secondary heat exchanger is
clogged. I've had enough experience of that one in the past, and
that's not the problem. I've cleaned out the secondary heat exchanger
- no better. So I replaced the secondary heat exchanger - no better!

So the question is, what else could cause this problem. It seems not
to be a fault with the (theormostatic) shower, because the same
happens when any tap(s) are opened, I've tried that one. Could it be
the pump failing, and not getting heat away quickly enough? Or I
guess the sensor thinking the DHW is hotter than it is, and shutting
down the boiler when it doesn't need to shut down? Or the PCB (which
seems to be the standard diagnosis when all else fails).

I could easily run up a bill of a couple of hundred in replacing
parts that don't need replacing, so any guidance would be welcome
before I start lining the pockets of the local plumbers' merchant.
Good thing it's summer.

While I appreciate its not the best time of the year for this, can it
run the rads ok?


OK, here's progress so far.

When a hot tap is open the flow rate is constant. The reason the water goes cold is that the boiler stops firing for a few seconds, then when it has cooled down, fires up again.

As for the water in the primary circuit, it could out-do Evian for purity. Although to be fair a few weeks ago if it was going to be packaged and sold in Tesco it would have been better off on the black treacle shelf. The system had a few problems which were documented in a post of mine several weeks ago. Part of the cure involved lashings of Fernox DS40 to clean everything out, followed by generous quantities of inhibitor, so now it's all clean and lovely.

Anyway, the good news is that I followed John's suggestion to see if the boiler can run the rads. It can. And having tried that out the hot water taps are now fine. Maybe there was some sort of blockage in the primary heat exchanger which a good old circulation cured, who knows. Anyway, it's working again.

Let's not get too excited yet, it could well go tits-up again before bedtime. But thanks to all (including the lieutenant who at least made me laugh).

Cheers!

Martin

On 07/07/2012 21:27, Martin Pentreath wrote:
On Saturday, July 7, 2012 7:15:36 PM UTC+1, John Rumm wrote:
On 07/07/2012 15:54, Martin Pentreath wrote:
Hi to all,

My combi is on the blink. It's an Ariston Microgenus - the old
model, it's not a condensing boiler.

Symptoms: shower oscillates between hot and cold. In fact so do
any of the taps when opened. Aha! Clearly the secondary heat
exchanger is clogged. I've had enough experience of that one in
the past, and that's not the problem. I've cleaned out the
secondary heat exchanger - no better. So I replaced the secondary
heat exchanger - no better!

So the question is, what else could cause this problem. It seems
not to be a fault with the (theormostatic) shower, because the
same happens when any tap(s) are opened, I've tried that one.
Could it be the pump failing, and not getting heat away quickly
enough? Or I guess the sensor thinking the DHW is hotter than it
is, and shutting down the boiler when it doesn't need to shut
down? Or the PCB (which seems to be the standard diagnosis when
all else fails).

I could easily run up a bill of a couple of hundred in replacing
parts that don't need replacing, so any guidance would be
welcome before I start lining the pockets of the local plumbers'
merchant. Good thing it's summer.

While I appreciate its not the best time of the year for this, can
it run the rads ok?


OK, here's progress so far.

When a hot tap is open the flow rate is constant. The reason the
water goes cold is that the boiler stops firing for a few seconds,
then when it has cooled down, fires up again.

As for the water in the primary circuit, it could out-do Evian for
purity. Although to be fair a few weeks ago if it was going to be
packaged and sold in Tesco it would have been better off on the black
treacle shelf. The system had a few problems which were documented in
a post of mine several weeks ago. Part of the cure involved lashings
of Fernox DS40 to clean everything out, followed by generous
quantities of inhibitor, so now it's all clean and lovely.

Anyway, the good news is that I followed John's suggestion to see if
the boiler can run the rads. It can. And having tried that out the
hot water taps are now fine. Maybe there was some sort of blockage in
the primary heat exchanger which a good old circulation cured, who
knows. Anyway, it's working again.

If its been refilled recently, it could have been air in the primary
then... If you were unlucky, and some of that air was in the main HE,
the "bubble" would have been recirculating round the boiler periodically
on a fairly short time signature when in DHW mode.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Hysteresis.

Obviously things are taking too long for the control loop and this manifests
itself as oscillation.
Where that item is is going to be hard to judge.

Brian

--
From the Bed of Brian Gaff.
The email is valid as
Blind user.
"Martin Pentreath" wrote in message
...
Hi to all,

My combi is on the blink. It's an Ariston Microgenus - the old model, it's
not a condensing boiler.

Symptoms: shower oscillates between hot and cold. In fact so do any of the
taps when opened. Aha! Clearly the secondary heat exchanger is clogged. I've
had enough experience of that one in the past, and that's not the problem.
I've cleaned out the secondary heat exchanger - no better. So I replaced the
secondary heat exchanger - no better!

So the question is, what else could cause this problem. It seems not to be a
fault with the (theormostatic) shower, because the same happens when any
tap(s) are opened, I've tried that one. Could it be the pump failing, and
not getting heat away quickly enough? Or I guess the sensor thinking the DHW
is hotter than it is, and shutting down the boiler when it doesn't need to
shut down? Or the PCB (which seems to be the standard diagnosis when all
else fails).

I could easily run up a bill of a couple of hundred in replacing parts that
don't need replacing, so any guidance would be welcome before I start lining
the pockets of the local plumbers' merchant. Good thing it's summer.

Cheers!

Martin