# Low pressure/pump fault



## derrick (Mar 31, 2011)

I have a baxi 30/85 boiler which shows a "Low pressure/pump fault" flashing neon light. The pressure is not low. It shows between 1 and 2 bar on the pressure gauge. A first it was an intermittent problem and the boiler wouldn't fire. Turning the power off and back on a couple of times would get the boiler to start. I was advised to change the diaphragm in the hydraulic pressure valve and this made things worse. It now won't fire at all. I changed the pressure valve and this didn't help either. I now have to turn on the boiler, wait for the central heating light to come on , then pull out the micro switch on the pressure valve and the boiler fires up. The problem is, the pin which activates the micro switch won't come out to activate it. I checked the pump and it runs so I'm nearly sure that's not the problem. I checked the expansion vessel and I didn't get any water coming out when I pressed the valve. I re pressurised the expansion vessel and the boiler still doesn't fire. There is an automatic filling valve which I presume has a non-return valve. I closed the gate valve after it in case to no avail. What else could cause this problem? I think I checked everything. Could there be a loss of pressure or fault in the cylinder coil?


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## plbgbiz (Aug 27, 2010)

There are some pretty savvy boiler folks in the Zone (not me :laughing. Help should be on it's way soon.


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## derrick (Mar 31, 2011)

Thanks. It's a tricky one.


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## hydronicsbob (Oct 6, 2010)

*some things to check.*



derrick said:


> "Low pressure/pump fault" flashing neon light. The pressure is not low. It shows between 1 and 2 bar on the pressure gauge. A first it was an intermittent problem and the boiler wouldn't fire. Turning the power off and back on a couple of times would get the boiler to start. I was advised to change the diaphragm in the hydraulic pressure valve and this made things worse. It now won't fire at all. I changed the pressure valve and this didn't help either. I now have to turn on the boiler, wait for the central heating light to come on , then pull out the micro switch on the pressure valve and the boiler fires up. The problem is, the pin which activates the micro switch won't come out to activate it. I checked the pump and it runs so I'm nearly sure that's not the problem. I checked the expansion vessel and I didn't get any water coming out when I pressed the valve. I re pressurised the expansion vessel and the boiler still doesn't fire. There is an automatic filling valve which I presume has a non-return valve. I closed the gate valve after it in case to no avail. What else could cause this problem? I think I checked everything. Could there be a loss of pressure or fault in the cylinder coil?


do you know what condition causes the "low pressure/pump fault"?
Is it a safety where if the pressure drops to below a certain point then it will shut-off to protect the boiler?

If this is the case, then you should look at the pressure reducing valve (hydraulic pressure valve) setting and what pressure is in the expansion tank (you have to check it when it is disconnected from the system). The two setting should be the same. Here is a good resource (click here).

When reading the literature - especially page 33 where it talks about the point of "no pressure change", and the pressure reducing valve and diaphragm style expansion tank.

From past experience I suspect you are on the borderline of pressure and if you are pumping towards the "point of no pressure change", then when the pump comes on it reduces the pressure below the threshold of the safety.

regardless if this is the problem, you need to have the diaphragm style expansion tank and the pressure reducing valve set at the same pressure to work right.


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