Potterton Promax gas pressure problem

[Jock Spanners]

Evening All,

I've been defeated by a Potterton Promax combi today and I'm a sore loser!
When there's a demand for heat it lights with an explosive ignition then it immediately shuts off and then repeats in a continuous cycle on/off. There's no fault code, the spark gap is correct and all electrical tests were okay. When I checked the inlet pressure I had only 16mb on the heating so I whipped off the valve and blew out the filter. It's all pointing to a gas pressure problem. There's 21mb wp at the meter. The boiler's in the kitchen with a gas hob and there's a gas fire in the living room. The customer has also complained about the fire going off regularly after 10 minutes or so. When I serviced the boiler in March it was at 18mb on hot water and now it's down to 14mb. All the pipework is buried in concrete. I just don't understand how the pressure has suddenly dropped and I'm not convinced it's not a valve or PCB fault. Any advice welcomed.

Jock

 

[Aquarius]

Any drop on TT? Any carbon deposits in gas line?

 

[Jock Spanners]

Any drop on TT? Any carbon deposits in gas line?

Not sure. It's buried underground

 

[Aquarius]

Not sure. It's buried underground

What do you mean? Have you carried out a tightness test? Carbon deposits will be evident by undoing the nut to gas inlet.

 

[Jock Spanners]

What do you mean? Have you carried out a tightness test? Carbon deposits will be evident by undoing the nut to gas inlet.

Yes. There were carbon deposits in the valve filter. The installation is tight.

 

[Aquarius]

I’d possibly be checking the meter regulator then, 21mbar working, but could be sticking, especially when you say the gas fire goes out. Light the hotplates on the hob and goes to fire boiler, if the hotplates extinguish, then I’d say meter regulator fault.

 

[Jock Spanners]

I’d possibly be checking the meter regulator then, 21mbar working, but could be sticking, especially when you say the gas fire goes out. Light the hotplates on the hob and goes to fire boiler, if the hotplates extinguish, then I’d say meter regulator fault.

I had Transco check the regulator and they okayed it. I think there must be some carbon deposits (or whatever) in a section of the pipe to the boiler. I'm thinking of using my 18 volt pump to try and push it through.

 

[EvilDrPorkChop]

Have you Gas rated it when the HW is on, and checked the CO readings? (Even with the 14mbar inlet) Possibility it's getting too much gas hence the low inlet.

 

[Jock Spanners]

Have you Gas rated it when the HW is on, and checked the CO readings? (Even with the 14mbar inlet) Possibility it's getting too much gas hence the low inlet.

The CO2% was spot on at 8.7. Not sure about CO ppm. Can check on Monday. Why would the inlet pressure be low if there was too much gas?

 

[EvilDrPorkChop]

The CO2% was spot on at 8.7. Not sure about CO ppm. Can check on Monday. Why would the inlet pressure be low if there was too much gas?

Your gas rate is your big one to check.

Well if you've got a 25kw boiler, on pipework sized for a 25kw boiler and it's burning 30kw the Inlet will be low...