Strange gas pressure drop

[denso13]

What I’m struggling to understand is, if pressure is so low as he said, how can the boiler still deliver burn rate 3.7 m3/h (under max load). i.e. the volume of gas delivered to the boiler under max load is still well within manufacture range (max 3.8 m3/h) despite the pressure being just over half of manufacturer’s working required level (9.5mbar vs 17mbar)??

Boilers frequently work ok at lower working pressures than specified.

 

[fixitflav]

What I’m struggling to understand is, if pressure is so low as he said, how can the boiler still deliver burn rate 3.7 m3/h (under max load). i.e. the volume of gas delivered to the boiler under max load is still well within manufacture range (max 3.8 m3/h) despite the pressure being just over half of manufacturer’s working required level (9.5mbar vs 17mbar)?? Or is there no relationship between volume burn and pressure?

I'd be a bit sceptical about the 9.5mb. My boiler needs about 10mb at the burner at design output, so if it's anything similar clearly 9.5mb is too low. There would be some pressure loss over the gas valve and the pressure at the burner, and boiler output would fall.
Boiler manual here in case you haven't got it. ecotec-installation-and-servicing1.pdf
If everything is in accordance with the regs minimum pressure at boiler inlet is 17.5mb. But I think most boilers will give full output with pressure a few mb lower.
The manual doesn't give gas pressure at the burner, just says 20mb inlet, repeated on page 22. My guess is they haven't put much thought into it and just quote the "nominal" supply pressure.

 

[CountryFan]

The manual doesn't give gas pressure at the burner, just says 20mb inlet, repeated on page 22. My guess is they haven't put much thought into it and just quote the "nominal" supply pressure.

It has an inlet working pressure, specified as a minimum value. Burner pressure can’t be measured being a Zero Governor.

 

[fixitflav]

It has an inlet working pressure, specified as a minimum value.

Do you mean the 20mb? Because it could be 17.5mb and meet the regs. Perhaps they say 20 to give themselves a getout, don't know whether they'd get away with it!

 

[CountryFan]

Do you mean the 20mb? Because it could be 17.5mb and meet the regs. Perhaps they say 20 to give themselves a getout, don't know whether they'd get away with it!

Yes I’m well aware of what pressure it can be. All manufacturers give a minim inlet working pressure, they’re not the ones installing them.

 

[fixitflav]

Yes I’m well aware of what pressure it can be. All manufacturers give a minim inlet working pressure, they’re not the ones installing them.

I wasn't trying to tell you anything you didn't know!
I remember seeing a boiler manual which specified an actual pressure requirement. I'll try to find it.

 

[Johntheo5]

Here's a bit of info from a Worcester Greenstar Compact..........

 

[fixitflav]

Here's a bit of info from a Worcester Greenstar Compact..........

View attachment 408110

Interesting. I haven't (yet) found a manual which gives actual required gas pressure, but several of them say 20mb (nominal) which is something!

 

[fixitflav]

What I’m struggling to understand is, if pressure is so low as he said, how can the boiler still deliver burn rate 3.7 m3/h (under max load). i.e. the volume of gas delivered to the boiler under max load is still well within manufacture range (max 3.8 m3/h) despite the pressure being just over half of manufacturer’s working required level (9.5mbar vs 17mbar)?? Or is there no relationship between volume burn and pressure?

My bad, the manual does give minimum inlet pressure, at the test point. It's on page 37, says 15mb for the ecoTEC plus 637. There'll be some loss before that point, gas iso valve etc. There doesn't appear to be test point upstream of that, so unless one is added on the pipe just before the boiler, can't compare the test point pressure with the 17.5mb regs figure.

 

[Daveydub]

What I’m struggling to understand is, if pressure is so low as he said, how can the boiler still deliver burn rate 3.7 m3/h (under max load)

He didn't say 3.7m3h he said 37m3h. I suspect that he meant 37kw and this is the figure that he got off the data plate.
You could gas rate it yourself and post the result here.
Run at maximum (have a tap or 2 open), take a meter reading and after 2 minutes take another reading.

 

[Razor900]

He didn't say 3.7m3h he said 37m3h. I suspect that he meant 37kw and this is the figure that he got off the data plate.
You could gas rate it yourself and post the result here.
Run at maximum (have a tap or 2 open), take a meter reading and after 2 minutes take another reading.

Running a hot tap will not get the boiler to maximum rate

 

[Daveydub]

Running at max rate will require a tap or 2 to be open though

 

[fixitflav]

Running at max rate will require a tap or 2 to be open though

No, it's a system boiler, not a combi

 

[Daveydub]

No, it's a system boiler, not a combi

Didn't spot that, ignore the bit about the taps.

 

[Razor900]

Didn't spot that, ignore the bit about the taps.

Sorry I couldn't resist lol

The gas supply is almost certainly well undersized if its 22mm at the meter.

But if they set D.0 to 15 the boiler will never run hard enough for it to matter and they will have more efficient heating that also heats up quicker.

The boiler is ridiculously oversized