Our hot water began to play-up when the boiler was just over a couple of years old and the problem continues to this day (3 years down the line). Annoyingly, we only changed the old one (10 year old Vailant combi) after repeated attempts by BG service people, including replacement of most major component, failed to fix exactly the same problem.

The problem is that the hot water is not reliably dispensed. When not produced on demand, the boiler is not firing-up properly. It makes a half-arsed attempt, with whirring of exhaust fan and a brief puff of steam, but at the tap, the water is cold or lukewarm. Sometimes, though, it plays ball and the hot water is fine.

Now here's the thing; if water is drawn simultaneously from a hot outlet and certain cold outlets and/or a second hot outlet, the boiler can usually be made to fire-up and away we go. In some cases, closing off those additional outlets causes the hot water to wane.

In the light of the observations described above, it seems to me that there might be an issue with water pressure, but it's not that the flow rate is too high for the boiler to heat the volume passing through the heat exchanger. I say this because i) draw from additional hot outlets can remedy it, ii) when it happens, the boiler isn't firing properly and iii) if anything, the problem tends to be worse in warmer weather.

I did, in fact, check our water pressure and found that while it was rather high, it fell within acceptable operational range for the boiler. Regardless, I wonder whether it's worth trying an adjustable pressure limiting valve on the boiler inlet. I'm more open to a sporting chance of a pragmatic solution rather than a dead certain lengthy investigation!

What do you think? Worth a try, or total waste of time?

Cheers. Terry.

On 12/04/2016 08:42, wrote:
Our hot water began to play-up when the boiler was just over a couple of years old and the problem continues to this day (3 years down the line). Annoyingly, we only changed the old one (10 year old Vailant combi) after repeated attempts by BG service people, including replacement of most major component, failed to fix exactly the same problem.

The problem is that the hot water is not reliably dispensed. When not produced on demand, the boiler is not firing-up properly. It makes a half-arsed attempt, with whirring of exhaust fan and a brief puff of steam, but at the tap, the water is cold or lukewarm. Sometimes, though, it plays ball and the hot water is fine.

Now here's the thing; if water is drawn simultaneously from a hot outlet and certain cold outlets and/or a second hot outlet, the boiler can usually be made to fire-up and away we go. In some cases, closing off those additional outlets causes the hot water to wane.

In the light of the observations described above, it seems to me that there might be an issue with water pressure, but it's not that the flow rate is too high for the boiler to heat the volume passing through the heat exchanger. I say this because i) draw from additional hot outlets can remedy it, ii) when it happens, the boiler isn't firing properly and iii) if anything, the problem tends to be worse in warmer weather.

I did, in fact, check our water pressure and found that while it was rather high, it fell within acceptable operational range for the boiler. Regardless, I wonder whether it's worth trying an adjustable pressure limiting valve on the boiler inlet. I'm more open to a sporting chance of a pragmatic solution rather than a dead certain lengthy investigation!

What do you think? Worth a try, or total waste of time?

Cheers. Terry.

If the pressure is within the acceptable range, then there must be a fault.

My Alpha combi has just had a similar problem fixed- it was a failed
diaphragm somewhere, and the part was about £30, labour £80 or so. It
manifested itself with the temperature fluctuating at first, then the
boiler failing to fire for hot water, or firng for a second or two and
stopping.

On Tuesday, 12 April 2016 08:43:00 UTC+1, wrote:
Our hot water began to play-up when the boiler was just over a couple of years old and the problem continues to this day (3 years down the line). Annoyingly, we only changed the old one (10 year old Vailant combi) after repeated attempts by BG service people, including replacement of most major component, failed to fix exactly the same problem.

The problem is that the hot water is not reliably dispensed. When not produced on demand, the boiler is not firing-up properly. It makes a half-arsed attempt, with whirring of exhaust fan and a brief puff of steam, but at the tap, the water is cold or lukewarm. Sometimes, though, it plays ball and the hot water is fine.

Now here's the thing; if water is drawn simultaneously from a hot outlet and certain cold outlets and/or a second hot outlet, the boiler can usually be made to fire-up and away we go. In some cases, closing off those additional outlets causes the hot water to wane.

In the light of the observations described above, it seems to me that there might be an issue with water pressure, but it's not that the flow rate is too high for the boiler to heat the volume passing through the heat exchanger. I say this because i) draw from additional hot outlets can remedy it, ii) when it happens, the boiler isn't firing properly and iii) if anything, the problem tends to be worse in warmer weather.

I did, in fact, check our water pressure and found that while it was rather high, it fell within acceptable operational range for the boiler. Regardless, I wonder whether it's worth trying an adjustable pressure limiting valve on the boiler inlet. I'm more open to a sporting chance of a pragmatic solution rather than a dead certain lengthy investigation!

What do you think? Worth a try, or total waste of time?

Cheers. Terry.

Combis can only modulate down so far, resulting in exactly the symptoms you describe. It's one reason I'm not that keen on them.


NT

On Tue, 12 Apr 2016 08:56:45 +0100, Chris Bartram
wrote:

On 12/04/2016 08:42, wrote:
Our hot water began to play-up when the boiler was just over a couple of years old and the problem continues to this day (3 years down the line). Annoyingly, we only changed the old one (10 year old Vailant combi) after repeated attempts by BG service people, including replacement of most major component, failed to fix exactly the same problem.


So the only common factor appears to be the high water pressure.

On 4/12/2016 12:25 PM, wrote:
On Tuesday, 12 April 2016 08:43:00 UTC+1, wrote:
Our hot water began to play-up when the boiler was just over a couple of years old and the problem continues to this day (3 years down the line). Annoyingly, we only changed the old one (10 year old Vailant combi) after repeated attempts by BG service people, including replacement of most major component, failed to fix exactly the same problem.

The problem is that the hot water is not reliably dispensed. When not produced on demand, the boiler is not firing-up properly. It makes a half-arsed attempt, with whirring of exhaust fan and a brief puff of steam, but at the tap, the water is cold or lukewarm. Sometimes, though, it plays ball and the hot water is fine.

Now here's the thing; if water is drawn simultaneously from a hot outlet and certain cold outlets and/or a second hot outlet, the boiler can usually be made to fire-up and away we go. In some cases, closing off those additional outlets causes the hot water to wane.

In the light of the observations described above, it seems to me that there might be an issue with water pressure, but it's not that the flow rate is too high for the boiler to heat the volume passing through the heat exchanger. I say this because i) draw from additional hot outlets can remedy it, ii) when it happens, the boiler isn't firing properly and iii) if anything, the problem tends to be worse in warmer weather.

I did, in fact, check our water pressure and found that while it was rather high, it fell within acceptable operational range for the boiler. Regardless, I wonder whether it's worth trying an adjustable pressure limiting valve on the boiler inlet. I'm more open to a sporting chance of a pragmatic solution rather than a dead certain lengthy investigation!

What do you think? Worth a try, or total waste of time?

Cheers. Terry.

Combis can only modulate down so far, resulting in exactly the symptoms you describe. It's one reason I'm not that keen on them.


NT


Agree, but I still think there is likely to be a fault in the control
system somewhere.

I suspect that gas repair guys increasingly follow automotive practice,
replacing one thing after another until they find the fix, then say that
they all needed replacing. (Not to deny that this is sometimes the
cheapest strategy when you include labour costs, and *some* of them
probably understand the engineering).

Pressure limiting valves are not expensive, and useful if your cold
water is a bit "lively". I used to have one, but I'd guess it isn't the
problem here.

What is the flow rate at the hot tap?

"newshound" wrote in message
...
On 4/12/2016 12:25 PM, wrote:
On Tuesday, 12 April 2016 08:43:00 UTC+1, wrote:
Our hot water began to play-up when the boiler was just over a couple of
years old and the problem continues to this day (3 years down the line).
Annoyingly, we only changed the old one (10 year old Vailant combi)
after repeated attempts by BG service people, including replacement of
most major component, failed to fix exactly the same problem.

The problem is that the hot water is not reliably dispensed. When not
produced on demand, the boiler is not firing-up properly. It makes a
half-arsed attempt, with whirring of exhaust fan and a brief puff of
steam, but at the tap, the water is cold or lukewarm. Sometimes, though,
it plays ball and the hot water is fine.

Now here's the thing; if water is drawn simultaneously from a hot
outlet and certain cold outlets and/or a second hot outlet, the boiler
can usually be made to fire-up and away we go. In some cases, closing
off those additional outlets causes the hot water to wane.

In the light of the observations described above, it seems to me that
there might be an issue with water pressure, but it's not that the flow
rate is too high for the boiler to heat the volume passing through the
heat exchanger. I say this because i) draw from additional hot outlets
can remedy it, ii) when it happens, the boiler isn't firing properly and
iii) if anything, the problem tends to be worse in warmer weather.

I did, in fact, check our water pressure and found that while it was
rather high, it fell within acceptable operational range for the boiler.
Regardless, I wonder whether it's worth trying an adjustable pressure
limiting valve on the boiler inlet. I'm more open to a sporting chance
of a pragmatic solution rather than a dead certain lengthy
investigation!

What do you think? Worth a try, or total waste of time?

Cheers. Terry.

Combis can only modulate down so far, resulting in exactly the symptoms
you describe. It's one reason I'm not that keen on them.


NT


Agree, but I still think there is likely to be a fault in the control
system somewhere.

I suspect that gas repair guys increasingly follow automotive practice,
replacing one thing after another until they find the fix,

That isnt how automotive practice is done anymore.

The diagnostic system says what has failed and that is replaced.

then say that they all needed replacing. (Not to deny that this is
sometimes the cheapest strategy when you include labour costs, and *some*
of them probably understand the engineering).

Pressure limiting valves are not expensive, and useful if your cold water
is a bit "lively". I used to have one, but I'd guess it isn't the problem
here.

On 12/04/2016 08:42, wrote:

Now here's the thing; if water is drawn simultaneously from a hot
outlet and certain cold outlets and/or a second hot outlet, the
boiler can usually be made to fire-up and away we go. In some cases,
closing off those additional outlets causes the hot water to wane.

What do you think? Worth a try, or total waste of time?

It sounds like the flow / diaphragm switch that detects the flow of hot
water is not working as it should.


--
Cheers,

John.

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What do you think? Worth a try, or total waste of time?

It sounds like the flow / diaphragm switch that detects the flow of hot
water is not working as it should.



I had a flow problem and it was caused by a degraded o ring in the flow
sensor - at certain flow rates it got drawn into the flow and reduced it.

On 12/04/2016 08:56, Chris Bartram wrote:

If the pressure is within the acceptable range, then there must be a fault.

It's not just pressure but flow rate that matters. The pressure
might drop too low once the required flow rate is reached.

You need to refer to the manufacturers website and see what
the minimum delivery is per minute. There are special measuring
jugs for this pupose but any graduated container will do.

Now here's the thing; if water is drawn simultaneously from a hot outlet and certain cold outlets and/or a second hot outlet, the boiler can usually be made to fire-up and away we go. In some cases, closing off those additional outlets causes the hot water to wane.

When hot water is drawn off the Worcester Bosch Greenstar combi boiler turbine rotates and sends a voltage to the printed circuit board. If the turbine is not rotating correctly/sticking/defective it will cause this issue.
sometimes thermostatic shower mixers hot water flows section flows into the cold water section will cause a fault similar to what you are describing.

www.worcesterboilerrepairs.com
Mohun
Repaired and serviced thousands of Worcester Boilers
Registered Gas Safe engineer