boiler operating pressure measurement, ideal boiler.

cascas · Posted: Fri Feb 24, 2012 11:53 pm

On a ideal logic boiler, as far as I know there is only one test point for gas pressure on the incoming isolation valve/integral testpoint.

Operating pressure is showing as 18mbar which seems a little low. The manual states that The external gas cock could further reduce the operating pressure when measured at its test point. The pressure drop is relative to the heat input to the boiler (kW) (approx 1.5mbar),

I have come across WB boilers where there is a pressure drop between the isolation valve and the gas valve, but cannot see how the boiler could affect the measurement at the isolation valve. Has anyone else got experience of these ideal boilers?

gaswizzard · Posted: Sat Feb 25, 2012 12:47 am

Are you referring to a premix burner? (zero governor)

cascas · Posted: Sat Feb 25, 2012 1:01 am

gaswizzard wrote:

Are you referring to a premix burner? (zero governor)

yes.

gaswizzard · Posted: Sat Feb 25, 2012 1:07 am

cascas wrote:

I have come across WB boilers where there is a pressure drop between the isolation valve and the gas valve?

Not uncommon to see a pressure drop between isolation valve and inlet pressure test point on gas valve , if a premix then you will see a negative pressure reading at burner pressure test point.

cascas · Posted: Sat Feb 25, 2012 6:30 pm

I refer to the Ideal Independent (logic) rated at 33.7kw gross (30.4 nett)

The working pressure at the meter is 21mbar, and at the test point on the boiler 18mbar

I have gas rated the boiler and obtained a measurement of 2.91m3/hr. The MI show a gas rate of 3.13m3/hr (based on a cv of 38.7), so around 7% below MI. If adjusted for CV that the expected gas rate is around 3.03 – or the achieved rate is approx. 4% below theoretical. Both within a tolerance -10% / +5%

Without fitting a test point on the pipework, it not possible to confirm pressure loss over the pipework,

Is the supply undersized as I suspect, or does the inlet test point on the ideals give a low reading. (it shouldnt as it on on the isolation cock, rather than the gas valve)?

simond · Posted: Sat Feb 25, 2012 8:41 pm

Are you a registered installer?

Do you have a combustion analyser, use of this may enable you to adjust the boiler to give the correct gas rate.

gaswizzard · Posted: Sat Feb 25, 2012 9:40 pm

Exactly , burner maybe running a tad lean , CO2% maybe a tad low hence the lean burn , unless you know how to use a FGA and interpret the ersults then you're p**sing in the wind.

gaswizzard · Posted: Sat Feb 25, 2012 9:49 pm

cascas wrote:

I have gas rated the boiler and obtained a measurement of 2.91m3/hr. The MI show a gas rate of 3.13m3/hr (based on a cv of 38.7), so around 7% below MI. If adjusted for CV that the expected gas rate is around 3.03 – or the achieved rate is approx. 4% below theoretical. Both within a tolerance -10% / +5%

Based on a CV of 38.7 and a gas rate of 2.91 m3/h gross input would be around 31.12 kw/hr , 3.13m3/hr would be around 33.64 kw/hr.

shambolic · Posted: Sun Feb 26, 2012 5:01 pm

Take the screw right out as reading can be low due to this. Also check pipe size and run. As for co2 readings etc you can't and must not attempt to adjust as gas valve is fixed.

patsmotors · Posted: Sun Feb 26, 2012 6:38 pm

where is Agile,you can never find an Agile when you need one.

Combustion chamber question,i think.

gaswizzard · Posted: Sun Feb 26, 2012 7:22 pm

patsmotors wrote:

where is Agile,you can never find an Agile when you need one.

Combustion chamber question,i think.

Why is that? , nothing has been said that isn't in the MIs , considering the MIs are left with the end user then no problem.

patsmotors · Posted: Sun Feb 26, 2012 7:59 pm

Agile knows best.

gaswizzard · Posted: Sun Feb 26, 2012 9:10 pm

Again what's your point?