Three days ago I installed a Grundfos Alpha 2 pump. Initially all appeared to be well and the system starts up and runs well for 2 hours in the morning. However if we turn the heating on around 2pm then by about 6pm the heating system has stopped and the pump shows “ - - “ on the LCD display. Increasing the thermostat set point will not restart the pump and the only way to get everything going again is to power the whole system down for several seconds and restart it. The pump then appears to run OK for a while but then goes back to the “ - - “ display. The pump is running in the Auto mode and usually displays around 20+ watts when running. Any ideas please?
Problem with Grundfos Alpha 2 pump stalling
- Thread starter BGT
- Start date
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According to the Alpha fault finding chart, "--" means:
a) Electricity supply failure. Might be too low. Check that the electricity supply falls within the specified range; or
b) pump blocked.
Use a multimeter to check the voltage going into the pump when the problem occurs. If it is below 240v, it is probably a wiring fault - post details of your system for a diagnosis and repair advice.
The Alpha pumps are supposed to be self-unblocking; they do not have the silver screw in the middle like the older pumps.
a) Electricity supply failure. Might be too low. Check that the electricity supply falls within the specified range; or
b) pump blocked.
Use a multimeter to check the voltage going into the pump when the problem occurs. If it is below 240v, it is probably a wiring fault - post details of your system for a diagnosis and repair advice.
The Alpha pumps are supposed to be self-unblocking; they do not have the silver screw in the middle like the older pumps.
I agree that they are the meanings of that error code but I do not understand why it runs OK and then there would be a voltage drop and recover when I switch it all off and back on. Same goes for the blocked pump, expecially when it is a new pump and the old one showed no sign of problems.
It is a sealed, pressurised system running around 1 bar. It is an 8 year old Potterton Profile boiler recently serviced by BGas. There are diverter valves for hot water and central heating and a manual bypas valve. The thermostat is a Honeywell DT92E wireless unit installed a couple of months ago. The programmer is a Drayton Lifestyle installed about a year ago. There are TRVs on all except one rad.
The system was running well, but noisey and hard to balance until the Alpha 2 was installed. Now it is quite and heating all the rads when it is running.
It is a sealed, pressurised system running around 1 bar. It is an 8 year old Potterton Profile boiler recently serviced by BGas. There are diverter valves for hot water and central heating and a manual bypas valve. The thermostat is a Honeywell DT92E wireless unit installed a couple of months ago. The programmer is a Drayton Lifestyle installed about a year ago. There are TRVs on all except one rad.
The system was running well, but noisey and hard to balance until the Alpha 2 was installed. Now it is quite and heating all the rads when it is running.
I agree it's unlikely to be a blockage causing the problem; which just leaves a voltage drop,
Are there two valves (left) or one valve (right)?
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The Potterton profile has pump overrun, which is controlled by a thermostat in the boiler. The pump needs to be wired directly to the boiler. Did you do this? The thermostat could have failed; you need to monitor the voltage while the pump is working and when it stops.
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There are two diverter valves and the pump is wired directly to the boiler. The thermostat appears to be working fine as it is showing boiler demand at the appropriate temperatures. Measuring the voltage at the pump will be difficult with the type of connector they use, but I will try to measure that next time it happens. It ran OK yesterday.
So you have two valves as in the picture on the left? For future reference, that is a zone valve. The one on the right is a diverter valve.
I was not talking about the room thermostat or the temperature control thermostat on the boiler. I was referring to the pump overrun thermostat, which is inside the boiler. The purpose of this is to keep the pump running for several minutes after the boiler goes out; it stops the boiler overheating. This thermostat can go wrong and cause the problem you have.
Do both zone valves end up closed during the overrun period and if so is the bypass working as it should?
Turned out to be a faulty pump which has been replaced under warranty. The replacment seems to be running well.
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