@drdp – have you considered turning off your compensation and setting a manual flow temperature point.

Remember that your heat pump is aiming to deliver a target temperature for your house (usually 21C) so your weather compensation will adjust your heat pump but not your internal temperature.

Depending on your insulation, maybe start with a flow temperature of 35C. That shouldn't blast heat and it'll keep your heat pump running efficiently. You should see a decrease in room temperature with outside temperatures below 7C.

@editor hey Mars, thanks for the reply.

im not sure it’s possible to do this with the SMO 05. 

I think my problem is slightly different. I’ve been watching the compressor starts and can say with more confidence that the system is only heating hot water and overnight it only turns on twice for total of 2 hours for example.

the compressor is only active when the system valve is set to hw. The line temp goes up to 45 and heats the water. After this the compressor stops, the system goes back to the ch valve setting but the flow temp stays at 45 and then slowly drops down over a few hours. 

is it possible that when heating the hot water the system has enough residual heat to then heat the underfloor? I don’t understand how this would work as I thought they were separate systems and separate buffer tanks

@drdp, I’m not sure why it would be doing that. Maybe @heacol can shed some light.

@drdp Hi, Difficult to determine what is wrong, can you PM me a system drawing listing all components and wiring if possible. It does not seam to be working like it should, there may be a problem with the diverting valve.

@heacol thanks for the offer but unfortunately I’m not an engineer and have no idea how this is wired up 🙁 

im new to the property and any wiring diagrams they had are long gone. I could send photos of the system but I imagine that’s little help. 
oh and I can’t do yet as I’m still brand new to this forum and need a few more posts.

thanks for being so helpful! This forum is ace

There is slightly more to the story now. I’ve managed to time it right and get to the system when the compressor is on. Again this is only happening in hw mode. I held on to the blue underfloor pipes where they are exposed and a couple of them were really warm.

It seems that rather than just residual ch heat going in to the underfloor, the system is actually heating some of the underfloor the whole time it’s heating the hw. I assume it’s also putting this very hot water through my underfloor.

I think it’s time I called an engineer 

Posted by: @drdp

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There is slightly more to the story now. I’ve managed to time it right and get to the system when the compressor is on. Again this is only happening in hw mode. I held on to the blue underfloor pipes where they are exposed and a couple of them were really warm.

It seems that rather than just residual ch heat going in to the underfloor, the system is actually heating some of the underfloor the whole time it’s heating the hw. I assume it’s also putting this very hot water through my underfloor.

I think it’s time I called an engineer 

Before calling an Engineer, trace back along the warm pipework until you find the motorised 3-way diverter valve, or do you have two 2-way valves?

There should be a small lever on the side of the motor unit, try moving it back and forth to see if the valve is stuck. Watch the operation of the valve(s) with the system in both CH mode and DHW mode, they should divert the water flow one way and then the other.

@derek-m I think I have a 2-way diverter. It’s got 3 pipes going in to it and two positions (one input pipe and 2 output?).

I’ve been watching this valve and when the system is heating hw it’s in the right orientation and stays there, but at the same time the underfloor pipes are still getting hot. 

Do these systems have a heat “overflow”? I.e. if the hot water comes on, but it reaches temp quickly, would it divert some to the underfloor?

I know is sounds like I’m looking at things wrong, but I’m really really sure the physical valve and the SMO unit both say that are heating hw only, when in fact they are also sending heating to the floor

Posted by: @drdp

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@derek-m I think I have a 2-way diverter. It’s got 3 pipes going in to it and two positions (one input pipe and 2 output?).

I’ve been watching this valve and when the system is heating hw it’s in the right orientation and stays there, but at the same time the underfloor pipes are still getting hot. 

Do these systems have a heat “overflow”? I.e. if the hot water comes on, but it reaches temp quickly, would it divert some to the underfloor?

I know is sounds like I’m looking at things wrong, but I’m really really sure the physical valve and the SMO unit both say that are heating hw only, when in fact they are also sending heating to the floor

 

I suppose it should really be called a 3-port valve rather than a 3-way valve, but it would appear that is what is fitted. When operating correctly, it should divert the flow from the input port, to one or other of the outlet ports, but not to both at the same time. There could be some debris on the sealing face within the valve that is preventing it from shutting fully, or it may be sticking. Try selecting CH then DHW, to operate the valve, whilst gently tapping the valve body with a rubber mallet or suitable piece of wood.

@derek-m I think you've found the issue. I'll report back in a day or so to confirm but I'm pretty sure this is the issue.

The valve is a Honeywell UC4013 and it allows me to press on the valve directly. The value should be fully depressed to send water to the CH and it feels fine for 90% of the stroke and then sticky for the last 10%. It would make sense that when the unit thinks it's heating the hot water it's sending 10% of the heat to the floor.

This would explain why the house is roasting, why the bills are not ideal and why I never see the call for heat to the underfloor (it's already hot).

I'll have to read more and see if I can free up the valve without taking the system apart, otherwise it's still a call to the engineer.