Anyone know how one of these works?

Grundfos Central heating Pump

The reason for asking is we recently had out old failed pump replaced for this one. Beforehand we could get at least 2 hot baths from our hot water tank and had a decent supply of hot hot water.

Since this was fitted we do get hot water, but we struggle to get one bath. As we don't have a shower, lots of hot water is key.

Any ideas or guidance would be great.

Sound like the motorised valves sending water from the boiler to the pump aren't working properly so all the heat is going to the radiators.
Normally these valves divert the flow from the central heating to the heat exchanger in the hot water cylinder.

Could also be the thermostat on the hot water cylinder faulty and not sending a signal to the controller so the valves don't send water to it.

Heating pumps can be fitted either way, physically.

was it installed with the pump flow in the wrong direction ?. This would probably lead to ineffective stored water heating, and possibly increased cycling of the boiler itself ?.

Worth a thought ?

The pump is fairly straight forward. It either pumps or it doesn't. In my system the pump keeps running even if the thermostat has told the boiler to stop supplying heat. This assumes that the CH controller is on and demands hot water or CH. Normally you can select the speed, and therefore flowrate of the pump. I believe this pump has 3 speeds. Usually the pump has an isolation valve located on either side of it so that you do not have to drain the complete system to change the pump. Maybe one of these valves has not been opened fully after the pump was replaced and this is reducing the flowrate in the system. Possibly the pump may require to be bled. This can be done by turning the silver disc in the middle of the pump counter clockwise with a screwdriver until only water, not air, comes out. Please do this when the water is cold and also only turn the disc a small amount, as if you remove it you will get a huge amount of water exiting the hole.

To be honest any other fault-finding is difficult as it depends on the design of the rest of your system. Are there separate motorised valves for your radiators and hot water? Are they opening fully? If not they can usually be manually overridden etc etc.

I think I have probably confused the issue for you, but hopefully some of the above will help.

Les

Some good tips there...who installed the pump? Perhaps it was an 8 year old with a bit of guidance, as per the warning for the pump:


What was the spec of the old pump, you could compare the head/flow curves to check it is correct, but one would hope that it's been installed the correct way around, pumping in the same direction as the old one (clue: there's a big arrow on the side)