Central heating pump does not start at first when cold / rested

[Decscom]

I have a Grundfos Ups2 15-50/60 pump, approx 2 years old (still under warranty) which does not start when the system is cold or has not been calling for heat for a while, eg. first thing in the morning.

It makes a clicking noise every few seconds, then the boiler overheats, boiler thermostat cuts out and air travels around the system. When the air/vibration reaches the pump it usually starts or sometimes it just starts after a couple of minutes. Then once the boiler cools and restarts the system works through the day, although at first it sounds as if the boiler is on the point of overheating, sort of pre-boiling sound like a kettle.

I have bled the pump and tried turning the impeller before it starts in the morning and all seems well.

I assumed it was a fault with some aspect of the pump electronics.

The plumber came today and said he has not experienced this before. He can swap the pump but does not know if this will cure it and is not sure it will count as a warranty claim because it works most of the time and will be difficult to replicate the fault.

Anyone come across this before?

 

[Aire]

Strange one, did the plumber check the electrics over? When power is sent to the pump it will start instantly. If electrics are all ok then a new pump will be required.

 

[Decscom]

When the heating or hot water is calling for heat the three way valve operates and the green speed indicator light on the pump comes on but does not start. The plumber wanted to test if there was 240v present at the pump but before he could are the cover off the impeller started. The pump will run at all three speeds so is getting a supply once started and I assume if the green light is on then there is a supply as soon as the alive operates. I have only been aware of it in the morning and once in the afternoon. It is only apparent because of the boiler overheating sending air noisily around the pipe work including causing the water to come out of the expansion tank overflow. It seems as if it is caused when either the water in the pump has cooled or if it has been unused for a while. The house is occupied during the day and so the boiler is firing up frequently.

 

[Aire]

It's unlikely to be anything other than a faulty pump motor. If it's under warranty there should be reason not to swap it.

 

[Decscom]

Thanks. That was my conclusion. It just seemed odd that the plumber was not sure so I thought they might be something else to consider.

 

[Aire]

Thanks. That was my conclusion. It just seemed odd that the plumber was not sure so I thought they might be something else to consider.

It's probably the plumbers own confidence causing the issue. No one wants to wrongly diagnose an issue and charge for work that won't fix the problem and if he's not came across the issue before that will further add to his own doubts.