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That's a really useful observation, thanks very much @RobLe, there's no ice, pipes are well insulated. Now I just have to work out how to increase the flow rate..

Lots to think about, I really appreciate everyone's input. Obviously a lot to learn! I'm going to try that, good suggestion. Why do you think that? In theory extracting heat directly from lake or river water, which this effectively is, is supposed to be much more efficient... great, thanks for that, looks like an excellent idea. Yes, you may well be right there, I need to work out what the optimal flow rate should be, the (dirty) ground water doesn't go directly to the heat pump, its pumped through a brazed plate heat exchanger then back into the water table some distance away from the extraction. At that point it's 2 - 3 C cooler. There's a short 'brine' (glycol) closed loop between that and the heat pump. I don't think that's a problem, currently the ground water return is 6.5C This might help, there are temp sensors on each port of the heat exchanger plus an outside air temp one (darker blue). I think it shows the glycol circuit (black and pale blue) extracts up to 9 C which seems very effective, any thoughts? :-

It's Kelmscott, same Thames but further upstream near Lechlade It's a Danfoss/Thermia which doesn't have any way of calculating COP built in. Fortunately yes, we're in exactly the same situation, the house was built on a hump in 1947 after a big flood That's interesting, 200kWh might be an overestimate, there's only two, sometimes three of us. I'll dig out our old oil bills, that's a good idea. Currently rads are about 35-45 C with an outside temp of -1 C House is generally about 20 C You're right, GSHP's are supposed to be much more efficient than that. The borehole has a 750W pump which may well contribute a fair bit to the 200kWh. That's a really sensible thing to do. Yes that's right, the river is normally about 300 metres away. The house originally had a shallow well for drinking water .

@SteamyTea - There's certainly plenty of water around at the moment 🙂 Attached a view of the road from the front gate yesterday! Fortunately gone down today. Even when there's a drought the water table has never dropped too far to affect the water flow from the borehole, I guess its more like an underground river we've tapped into. Filters are clean there's no issues with flow rate and the heat exchanger, which stops the dirty water reaching the heat pump, is regularly reverse flushed.

Thanks for your interest @ProDave. Briefly, it's a 1940's stone built mid terrace 3/4 bed house about 120 sq m. including a 15 year old kitchen extension The heat pump is a Danfoss DHP Opti Pro 8 SP rated at “heating capacity B0/W35” = 7.51kW The water source is a 4m borehole, we are close to the river on sand and gravel, the water table is about 1-2 m below ground. It varies between 5 and 12 C currently 6.5 C, air temp today was between -2 and +4 C Radiators mostly connected with 22mm feed from a buffer tank to central manifold then microbore, seems to be well designed. Extn has 15mm pipework with two rads. The total heat demand was calculated by the installer to be 16,000kWh per year. I estimate that the heat pump uses approx 1,600kWh per month when it is cold and an average of 1,000kWh per month in Autumn and Spring. In summer it's about 200kWh per month.

Hi Just joined the forum to research ways of improving the efficiency and costs of running our heat pump. It's proved to be much more expensive to run than predicted. The original installer went bust shortly after commissioning it and I can't find anyone who I feel I can trust and has the expertise to investigate the situation I need to research and understand what needs to be done myself. I'm hoping to find some advice and learn from the experiences of others who I'm sure are going through similar issues.