Boiler overrun
 

In have been running the cottage heating on tick-over (all the roomstats
set to 15 deg. C)
Yesterday I found the system had depressurised!

Apart from the panic about screws through underfloor heating pipes:-)
what would happen to a W plan system during a power outage?
The Veissman boiler has several minutes of circulation on the internal
pump and the system is happy with DHW thermostat reaching set
temperature and there being no call for room heating.

Based on the thermal expansion figures and discussion in here I
calculated that the vessel fitted in the boiler would do the job. There
was a fair bit of teeth sucking from the boiler installers but they
didn't offer any alternative calculations.

Looking at the sizing tables from the vessel manufacturers, I am a fair
bit under the recommendations. Could this be why?
--
Tim Lamb

Boiler overrun
 

On Sunday, 10 February 2019 19:33:38 UTC, Tim Lamb wrote:

what would happen to a W plan system during a power outage?

everything stops & goes out, except the pilot light if a boiler has one. What is the unknown there?

The Veissman boiler has several minutes of circulation on the internal
pump and the system is happy with DHW thermostat reaching set
temperature and there being no call for room heating.

Based on the thermal expansion figures and discussion in here I
calculated that the vessel fitted in the boiler would do the job. There
was a fair bit of teeth sucking from the boiler installers but they
didn't offer any alternative calculations.

Looking at the sizing tables from the vessel manufacturers, I am a fair
bit under the recommendations. Could this be why?

You can always leave some air in the top of a large enough radiator.


NT

Boiler overrun
 

In message ,
writes
On Sunday, 10 February 2019 19:33:38 UTC, Tim Lamb wrote:

what would happen to a W plan system during a power outage?

everything stops & goes out, except the pilot light if a boiler has
one. What is the unknown there?

Er.. whether the thermal energy in the heat exchanger is sufficient to
overpressure the system with no circulation.

The Veissman boiler has several minutes of circulation on the internal
pump and the system is happy with DHW thermostat reaching set
temperature and there being no call for room heating.

Based on the thermal expansion figures and discussion in here I
calculated that the vessel fitted in the boiler would do the job. There
was a fair bit of teeth sucking from the boiler installers but they
didn't offer any alternative calculations.

Looking at the sizing tables from the vessel manufacturers, I am a fair
bit under the recommendations. Could this be why?

You can always leave some air in the top of a large enough radiator.

I could if there were any:-) Fully underfloor system. Curiously, I am
almost certain there is a second pressure vessel inside the thermal
store DHW tank.
--
Tim Lamb

Boiler overrun
 

On 10/02/2019 19:33, Tim Lamb wrote:
In have been running the cottage heating on tick-over (all the roomstats
set to 15 deg. C)
Yesterday I found the system had depressurised!

Apart from the panic about screws through underfloor heating pipes:-)
what would happen to a W plan system during a power outage?
The Veissman boiler has several minutes of circulation on the internal
pump and the system is happy with DHW thermostat reaching set
temperature and there being no call for room heating.

Based on the thermal expansion figures and discussion in here I
calculated that theÂ* vessel fitted in the boiler would do the job. There
was a fair bit of teeth sucking from the boiler installers but they
didn't offer any alternative calculations.

Looking at the sizing tables from the vessel manufacturers, I am a fair
bit under the recommendations. Could this be why?

The way to tell would be to use a rubber band and a sandwich bag tied
over the end of the pressure relief pipe. If at any point it does vent,
you would see some water collected in the bag. (normally it would remain
empty).


--
Cheers,

John.

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Boiler overrun
 

On 10/02/2019 20:40, Tim Lamb wrote:
In message ,
writes
On Sunday, 10 February 2019 19:33:38 UTC, Tim LambÂ* wrote:

what would happen to a W plan system during a power outage?

everything stops & goes out, except the pilot light if a boiler has
one. What is the unknown there?

Er.. whether the thermal energy in the heat exchanger is sufficient to
overpressure the system with no circulation.

The pump overrun is there to remove the excess heat from the boiler.

The worst a powercut can do on a W plan is cause an overheat trip on the
boiler stat.


--
Adam

Boiler overrun
 

In message , John
Rumm writes
On 10/02/2019 19:33, Tim Lamb wrote:
In have been running the cottage heating on tick-over (all the
roomstats set to 15 deg. C)
Yesterday I found the system had depressurised!
Apart from the panic about screws through underfloor heating
pipes:-) what would happen to a W plan system during a power outage?
The Veissman boiler has several minutes of circulation on the
internal pump and the system is happy with DHW thermostat reaching
set temperature and there being no call for room heating.
Based on the thermal expansion figures and discussion in here I
calculated that the* vessel fitted in the boiler would do the job.
There was a fair bit of teeth sucking from the boiler installers but
they didn't offer any alternative calculations.
Looking at the sizing tables from the vessel manufacturers, I am a
fair bit under the recommendations. Could this be why?

The way to tell would be to use a rubber band and a sandwich bag tied
over the end of the pressure relief pipe. If at any point it does vent,
you would see some water collected in the bag. (normally it would
remain empty).

This has happened once in about 4 months! The consumer unit is next to
the boiler so I can knock the power off while the boiler is running full
chat and watch the pressure gauge.

I'm just gathering the intestinal fortitude to try it:-)

--
Tim Lamb

Boiler overrun
 

In message , ARW
writes
On 10/02/2019 20:40, Tim Lamb wrote:
In message ,
writes
On Sunday, 10 February 2019 19:33:38 UTC, Tim Lamb* wrote:

what would happen to a W plan system during a power outage?

everything stops & goes out, except the pilot light if a boiler has
one. What is the unknown there?
Er.. whether the thermal energy in the heat exchanger is sufficient
to overpressure the system with no circulation.

The pump overrun is there to remove the excess heat from the boiler.

The worst a powercut can do on a W plan is cause an overheat trip on
the boiler stat.

Hmm.. the only symptom of an issue was the unexpected zero pressure
reading. Fired up and operated normally without any other adjustments.



--
Tim Lamb