My boiler (an Ariston Microgenus 27) has developed an intermitent
fault. Sometimes I come home expecting a nice warm house to find the
place freezing, but the boiler whirring away quite happily to itself,
the burners coming on for a few seconds then going off again. When
it's in this state the flow pipe to the rads is hot, but the return is
cold. The LEDs on the boiler show that the heat exchanger has got up
to temperature, which presumably is why the burners keep cutting off.
I've found one way of solving this is to turn the radiator circuit
temperature control on the boiler right up. This seems to waken it
from it's little trance, it starts to heat the rads and then I can
turn the knob back down and all is well (until next time this happpens
a few days later).

I think this might be a failed (or failing) bypass valve (which is an
integral part of this boiler). There's no legitimate reason why the
bypass should have kicked in - the rads are all on, the TRVs are
demanding heat because the place is like Siberia, and anyway there's
one rad with no TRV. What do people think of this diagnosis? The only
reason I'm doubtful is that I'm not sure that the flow pipe should be
getting so hot. Surely if the bypass has kicked in the water should
just be circulating within the boiler? And why would turning the
temperature knob up solve the problem?

"Martin Pentreath" wrote in message
om...
My boiler (an Ariston Microgenus 27) has developed an intermitent
fault. Sometimes I come home expecting a nice warm house to find the
place freezing, but the boiler whirring away quite happily to itself,
the burners coming on for a few seconds then going off again. When
it's in this state the flow pipe to the rads is hot, but the return is
cold. The LEDs on the boiler show that the heat exchanger has got up
to temperature, which presumably is why the burners keep cutting off.
I've found one way of solving this is to turn the radiator circuit
temperature control on the boiler right up. This seems to waken it
from it's little trance, it starts to heat the rads and then I can
turn the knob back down and all is well (until next time this happpens
a few days later).

I think this might be a failed (or failing) bypass valve (which is an
integral part of this boiler). There's no legitimate reason why the
bypass should have kicked in - the rads are all on, the TRVs are
demanding heat because the place is like Siberia, and anyway there's
one rad with no TRV. What do people think of this diagnosis? The only
reason I'm doubtful is that I'm not sure that the flow pipe should be
getting so hot. Surely if the bypass has kicked in the water should
just be circulating within the boiler? And why would turning the
temperature knob up solve the problem?


Check that the zone valves aren't sticking or faulty. Check that the pump
is running properly and not over heating or flooded. Check that the boiler
thermostats are all working properly. Make sure the flue isn't blocked, or
that any fan, if assisted, isn't jammed or faulty. Make sure any room
stat's haven't been altered by mistake, or deliberately, and are shutting
the system down to soon.

Check the system is properly flooded with water by bleeding the system from
the top down. Check any by-pass valves are open to their correct position.

If all these are OK, then call an engineer and have the system serviced
properly.


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On Wed, 10 Nov 2004 10:19:38 -0800, Martin Pentreath wrote:

My boiler (an Ariston Microgenus 27) has developed an intermitent
fault. Sometimes I come home expecting a nice warm house to find the
place freezing, but the boiler whirring away quite happily to itself,
the burners coming on for a few seconds then going off again. When
it's in this state the flow pipe to the rads is hot, but the return is
cold. The LEDs on the boiler show that the heat exchanger has got up
to temperature, which presumably is why the burners keep cutting off.
I've found one way of solving this is to turn the radiator circuit
temperature control on the boiler right up. This seems to waken it
from it's little trance, it starts to heat the rads and then I can
turn the knob back down and all is well (until next time this happpens
a few days later).

I think this might be a failed (or failing) bypass valve (which is an
integral part of this boiler). There's no legitimate reason why the
bypass should have kicked in - the rads are all on, the TRVs are
demanding heat because the place is like Siberia, and anyway there's
one rad with no TRV. What do people think of this diagnosis? The only
reason I'm doubtful is that I'm not sure that the flow pipe should be
getting so hot. Surely if the bypass has kicked in the water should
just be circulating within the boiler? And why would turning the
temperature knob up solve the problem?

The diverter valve is a primer suspect for these symptoms.
It's probably getting stuck in the DHW mode position when you turn the
heat up a lot it frees up enough to move fully to the CH mode and start
heating the rads.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

"Ed Sirett" wrote in message
news
On Wed, 10 Nov 2004 10:19:38 -0800, Martin Pentreath wrote:

My boiler (an Ariston Microgenus 27) has developed an intermitent
fault. Sometimes I come home expecting a nice warm house to find the
place freezing, but the boiler whirring away quite happily to itself,
the burners coming on for a few seconds then going off again. When
it's in this state the flow pipe to the rads is hot, but the return is
cold. The LEDs on the boiler show that the heat exchanger has got up
to temperature, which presumably is why the burners keep cutting off.
I've found one way of solving this is to turn the radiator circuit
temperature control on the boiler right up. This seems to waken it
from it's little trance, it starts to heat the rads and then I can
turn the knob back down and all is well (until next time this happpens
a few days later).

I think this might be a failed (or failing) bypass valve (which is an
integral part of this boiler). There's no legitimate reason why the
bypass should have kicked in - the rads are all on, the TRVs are
demanding heat because the place is like Siberia, and anyway there's
one rad with no TRV. What do people think of this diagnosis? The only
reason I'm doubtful is that I'm not sure that the flow pipe should be
getting so hot. Surely if the bypass has kicked in the water should
just be circulating within the boiler? And why would turning the
temperature knob up solve the problem?

The diverter valve is a primer suspect for these symptoms.
It's probably getting stuck in the DHW mode position when you turn the
heat up a lot it frees up enough to move fully to the CH mode and start
heating the rads.

The diverter valve is electric on this model. For info, the new Ariston
combi now has a full 5 year guarantee.

On Wed, 10 Nov 2004 23:26:41 +0000, IMM wrote:


"Ed Sirett" wrote in message
news
On Wed, 10 Nov 2004 10:19:38 -0800, Martin Pentreath wrote:

My boiler (an Ariston Microgenus 27) has developed an intermitent
fault. Sometimes I come home expecting a nice warm house to find the
place freezing, but the boiler whirring away quite happily to itself,
the burners coming on for a few seconds then going off again. When
it's in this state the flow pipe to the rads is hot, but the return is
cold. The LEDs on the boiler show that the heat exchanger has got up
to temperature, which presumably is why the burners keep cutting off.
I've found one way of solving this is to turn the radiator circuit
temperature control on the boiler right up. This seems to waken it
from it's little trance, it starts to heat the rads and then I can
turn the knob back down and all is well (until next time this happpens
a few days later).

I think this might be a failed (or failing) bypass valve (which is an
integral part of this boiler). There's no legitimate reason why the
bypass should have kicked in - the rads are all on, the TRVs are
demanding heat because the place is like Siberia, and anyway there's
one rad with no TRV. What do people think of this diagnosis? The only
reason I'm doubtful is that I'm not sure that the flow pipe should be
getting so hot. Surely if the bypass has kicked in the water should
just be circulating within the boiler? And why would turning the
temperature knob up solve the problem?

The diverter valve is a primer suspect for these symptoms.
It's probably getting stuck in the DHW mode position when you turn the
heat up a lot it frees up enough to move fully to the CH mode and start
heating the rads.

The diverter valve is electric on this model. For info, the new Ariston
combi now has a full 5 year guarantee.

What I said applies regardless of how the diverter valve is moved.
I would add that even if the bypass valve was stuck fully open it there
would still be some pressure to drive the rads.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html