@mike-h

The simple way to check if your water pumps are operating in PWM mode is count the number of cables that are connected, if there are two then it is probably being operated in PWM mode.

To check whether the pumps are capable of PWM mode if they only have one cable connected, check the model number or post a photo.

Posted by: @craig1980

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@derek-m both pumps operate whichever room stat is turned up/down. Both receiver's mounted on the wall by the cylinder acknowledge signal when turned up individually so that seems okay. Odd that both pumps work? Heat pump also kicks in whichever is turned up.

 

Turning both off will turn off the heat pump and water pump. Turning just one off makes a few clicks and that's all that changes. Same instantaneous power usage. 

Without being able to see how it is actually piped up, I suspect that one pump is pushing the return water back to the heat pump, and hence required for either DHW heating or CH. The second pump is probably for the UFH.

Try the same exercise as described previously, but with DHW heating selected rather than CH.

A further thing to check is the position of the motorised valves, when the different thermostats are operated in the different operating modes, DHW or CH.

@derek-m I don't have under floor. 

The room stats don't have an option for dhw. That is set up on the controller as a schedule or manually on/off. The temp can be adjusted within the controller menu. 

Where might I find the motorised valves? Thanks 

Posted by: @craig1980

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@derek-m I don't have under floor. 

The room stats don't have an option for dhw. That is set up on the controller as a schedule or manually on/off. The temp can be adjusted within the controller menu. 

Where might I find the motorised valves? Thanks 

Hi Craig,

Sorry, I assumed that you would have UFH with a second water pump installed. So that may mean that you have a buffer tank or low loss header instead. Could you please try to identify all the items of equipment within your system, and how they are connected together.

@derek-m here's a pic of what I have.

So, two tanks above the main 150l cyclinder, the white one is an unvented cylinder expansion tank 18l, no idea what the other does but it appears to be plumbed via a pressure guage. 

Two internal room stats, Samsung 12kw gen 6 heat pump, Joule 150l UVC, Samsung gen 6 wired controller. Salamander water pump which activates when hot tap is turned on but the pump is connected to the feed from the cold water tank in the loft. We are gravity fed. 

Apparently it's a two zone system but when running just one or the other it isn't set up as upstairs and downstairs. When we had the flow temp at 45 one or two rads upstairs got hot and the others were very slightly warm. 

As for the pumps running when dhw is turned on, both pumps engage when dhw on and turn off when not required. 

Salamander make pumps for pressurised showers. Some have automatic pressure regularisation, which enables them to deliver hot and cold evenly when drawing from sources at different pressures.

I've zoomed in but can't read the Salamander part number. It's possible that it's related to your ASHP installation only peripherally in order to supply a bath/shower at a reasonable flow-rate. I doubt it has any aspect of 'control' from the rest of the HP system.

@transparent yeah, I used to have one that was twin impeller so had a hot and cold feed (2 inlet, 2 outlet). This one is single impeller. Cold water comes from header tank and feeds in to pump then into system via a mixer valve. I told the guy we had poor flow from cold feed in to the house as we are on old 1/4" black pipe from the mains and this was his solution. We get a good pressure through the shower still.

Let's label a few bits:

Posted by: @derek-m

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@mike-h

The simple way to check if your water pumps are operating in PWM mode is count the number of cables that are connected, if there are two then it is probably being operated in PWM mode.

To check whether the pumps are capable of PWM mode if they only have one cable connected, check the model number or post a photo.

Thanks. Just the one cable to each pump. The buffer tank means there is flow separation and I presume that makes a second pump necessary. With two pumps I also suspect that PWM mode would get quite complicated. 

I have attached a photo, which shows the Grundfos pump. 

@transparent you are correct, I was just adding the info for Derek. 👍

@mike-h

Can you provide a closeup of the pump nameplate.