Poor inlet pressure on newly installed Worcs 40CDI

[Pssst]

The other day i went along to help a guy who was having problems with a Worcs GS 40CDI which he had just installed.

The problem was that at the inlet test point on the GV,he was getting 7mb WP when the boiler was full on in engineering mode.

I set up guages on the ecv outlet and the meter outlet. The metter sounded like a bag of spanners and was of a make known to be problematic.

SP at SVC was around 25mb. With the clanky meter the WP at the SP was around 21mb and the WP at meter outlet was about 18

I stuck a new non clanky meter in and the reading on the outlet was now 20mb and at the boiler..it had risen to 10mb.

There was only the boiler fitted in the building on a run of about 15m of 28 tubing.

Blew it and no apparent obstruction.

Im thinking that there was an issue/possible obstruction of the test point on the Worcs GV...I left him to it..

 

[diamondgas]

A restricted test point will still let you know... eventually... the WP!

If reading is on the P1 of the gas valve then there could be a blocked filter to the valve at a guess? Otherwise suspect blockage to supply?

 

[village idiot]

He should tell WB that the boiler is buggard. Lets see what the WB tech guy comes up with?

 

[Pssst]

A restricted test point will still let you know... eventually... the WP!

If reading is on the P1 of the gas valve then there could be a blocked filter to the valve at a guess? Otherwise suspect blockage to supply?

Yes thats what i was thinking ..ie a partially blocked inlet test point outlet. The screw doesnt come all the way out. Without knowing the internal structure of the gas passages, i was theorising that if it is partially blocked,bearing in mind the boiler is running full bore in engineering mode, could the flow cause almost a venturi effect/negative suction on the inlet test point thus giving a false low reading? As i say,we disconnected the meter and the boiler connection and blew it and it seemed fine. My parting shot was that he should gas rate it to see how much fuel its burning compared to the manufs specs which would be a tad over 4 m3/hr..

 

[Deleted member 7121]

Try cutting a test point in just before boiler and like you say gas rate it.

 

[diamondgas]

... could the flow cause almost a venturi effect/negative suction on the inlet test point thus giving a false low reading? As i say,we disconnected the meter and the boiler connection and blew it and it seemed fine. My parting shot was that he should gas rate it to see how much fuel its burning compared to the manufs specs which would be a tad over 4 m3/hr..

When you gas rate it you'll probably find it's spot on max rate. With modern zero governors they aren't bothered what's on the inlet .. all they want to maintain is zero on the outlet! To do so they'll open fully, and 'suck' as much as they can to maintain the volume they require. If pipe sizing is undersized or a restriction is present then maintaining pressure is compromised! If the inlet pressure is to low then there's a chance that the fan isn't pulling enough gas through ... flame lift then occurs ... too much air and not enough gas!

That's my take anyhoo's 🙂 Been a while since I've been to school of gas 🙂

 

[Ermintrude]

Always find when under gassed gas rate is high and pressure low at boiler , so agree !

 

[Pssst]

When you gas rate it you'll probably find it's spot on max rate. With modern zero governors they aren't bothered what's on the inlet .. all they want to maintain is zero on the outlet! To do so they'll open fully, and 'suck' as much as they can to maintain the volume they require. If pipe sizing is undersized or a restriction is present then maintaining pressure is compromised! If the inlet pressure is to low then there's a chance that the fan isn't pulling enough gas through ... flame lift then occurs ... too much air and not enough gas!

That's my take anyhoo's 🙂 Been a while since I've been to school of gas 🙂

Yes..i had that it mind too ..i.e that irrespective of inlet pressure and working pressure, the control model will modulate the fan to deliver max heat output and therefore maximum negative pressure on the the injector/zero governor leading to an overly lean mixture. Presumably in extreme circumstances, eg flame lift or unsatisfactory combustion...the flame detection system will take the burner out although that wasnt happening in this case. Either way,its academic as i departed having discussed,and left him to it....