Gas rate 8kw under

[mitchellcook]

Hi everyone, i'm new to this site, only passed my ACS a few weeks ago so go easy on me please.:tounge_smile: Anyway I have a question which i'm sure you guys can help me with.

I was serviciing a wb greenstar 42CDi today. When i gas rated it, (obviousally in the service mode) it only came out at 34kw. A whole 8KW under. I double checked and it was still the same.

I carried out a working pressure at the meter and it was 18.5 mbar. I also checked the working pressure at the boiler and it was also 18.5mbar. The gas was supplied through 22mm with about a max length of 5 meters. I know working pressure at the meter should be 21 + or - 2, then allowance of 1mbar drop to appliance, so really the lowest acceptable working pressure at an appliance is 18mbar, and I have 18.5mbar.

The engineer i was with reckoned it may have needed a u16 meter, but I checked on wb website and it says it only needs a gas flow rate of 4.4m3/hr, which a u6 can deliver.

So would I be wright in thinking the injector is blocked or is there any other reason that could cause this.

Thanks in advance!
Mitchell

 

[Billy Bob Bob]

the 42 cdi only puts out about 35 kw so your gas rate is not far off

 

[mitchellcook]

Thanks a lot gas man! Unfortunately didn't have mi. What else would cause a gas rate to be low if working pressures and injector is fine? Cheers

 

[Billy Bob Bob]

dirty blocked burner or wrong injector but in your case your very close to 35kw so thats not really low,and i am not a fan of calibration modes either,they often run at what the mi,s want the fga result to reflect,try running it on dhw and putting the fga in the results would be very different to quoted figures

 

[mitchellcook]

Thanks for the advice!

 

[tamz]

It probably modulated down a bit while you were doing it.
Keep the hot tap on while in service mode to keep it running at full rate. The diverter is moved to a mid position when in service mode.

 

[sparra1100]

yep probs 35kw on heating and dhw will be 42 or thereabouts as tamz says probs modulating on heating and gasman no,s his stuff so go with him

 

[GrahamM]

Your only a bit off the Mark with your G/R. If your FGA readings are spot on I would not worry about it.
Using service mode can sometimes be a hit & a miss.
Did you have all TRV's, stats all up full and a hot tap on full in the service mode?

 

[Atouchofgas]

I went on Worcester training, stated to do g/r and fga. You could put into serv mode, pop out divertor head (only 12v! ) and run hw tap. Done a few times and it meets all the MI readings

 

[AlexGas]

18.5 mbar working pressure at the meter is a bit low to me.Ok, it's only by 0.5, but it's low.

From BS 6400:

10 Commissioning of the meter installation
10.1 Regulator
10.1.1 Checks
The installer shall ensure the following.
a) The regulator gives an operating pressure at the outlet of the
meter of between 19 mbar and 23 mbar at corresponding flow
rates between 6 m3/h and 0.5 m3/h. If the pressure is outside this
range an Ofgem approved meter installer (OAMI) shall follow the
procedure in 10.1.2.

 

[Roger Welton]

18.5 mbar working pressure at the meter is a bit low to me.Ok, it's only by 0.5, but it's low.

From BS 6400:

10 Commissioning of the meter installation
10.1 Regulator
10.1.1 Checks
The installer shall ensure the following.
a) The regulator gives an operating pressure at the outlet of the
meter of between 19 mbar and 23 mbar at corresponding flow
rates between 6 m3/h and 0.5 m3/h. If the pressure is outside this
range an Ofgem approved meter installer (OAMI) shall follow the
procedure in 10.1.2.

You can then have 1 mbar drop across pipework to appliance

 

[GrahamM]

18.5 mbar working pressure at the meter is a bit low to me.Ok, it's only by 0.5, but it's low.

Whats 0.5 mbar between friends? We will not worry too much about that will we?

As per Worcester. It may be acceptable and to have as low 16.5 mbar WP at gas valve inlet, subject to all operational checks being ok. The OP states he has 18.5 mbar at the boiler. This should be more than acceptable as per Worcester.