Hey everyone. Sorry for the length of this question.

I have a Daikin Altherma ASHP and generally am very happy with it, but I have 2 problems that have cropped up and not sure if they are connected.

Prob 1: We've had a hotwater flow fault for a while now and many attempts to fix it have proved fruitless. The ASHP works in conjunction with a solar thermal panel so in summer the solar heats the water and all is good. However, last year, after years of working properly, the ASHP hot water system throws up a flow fault. It was intermittent at first and is now everytime the ASHP is asked for hot water. The space heating works every time. The flow fault is just the hot water.

So the engineers clean the filters, change the pump, filddle with wiring and tinker around, but nothing works. The heating engineers say its not the heatpump so is a plumbing issue. After months of trying to find plumbers who know heatpumps (I live in a rural part of the country) I find a company. They think it is the diverter valve causing the problem. So they drain down the system and fit a new one (at great cost). The problem persists. Between the hot flow from the ASHP and the hotwater cylinder is the diverter valve, a solenoid valve (a safety for the solar thermal system) and some copper pipework.

So everyone is at a loss as to what is causing the issue. My question is for ideas, but also could it be the coil inside the hotwater cylinder getting furred up? Does that happen? We live in a very hard water area, but have a filter on water entering the house to combat some of the hardness.

Prob 2: It started this week after the diverter valve was changed (but I only noticed it then as the days have got colder). The ASHP only seems to make up to 34°C and then drops the temp back down. The heat pump also sounds like it is struggling. Has anyone experienced this before? Anyone have a possible idea of the problem?

I hope someone can help with either or both issues.

Thanks

We had an altherma HT (the 2-stage high temperature system). The outdoor unit heats to about 35 Deg and the indoor unit has a second heat pump that boosts to 70+Deg.

The indoor unit failed with a fault code that initially suggested low flow, we bled out air, cleaned the strainers and had the system power flushed to no avail. The temperature rose to ~35deg due to the outdoor unit but the indoor unit couldn't make it any hotter. In our case it then cut out with the fault code.

The installers discussed the fault code with Daikin and started replacing components including sensors, pump, refrigerant expansion valve. The next step would be replacing the heat exchanger, as temperature/pressure readings suggested that the outdoor refrigerant had leaked into the indoor circuit. Both the labour and parts were more expensive than our previous boilers, so it quickly got beyond being economic. They suggested replacing the whole indoor unit but a change of model was coming and there was no stock of ours left.

At that point we sold the house (unrelated reasons!)

Good luck!

OK here we go attached is the diagram of the heating/hotwater system. I'm now pretty convinced I have 2 issues. The original hotwater flow fault and now a low temp issue (which I have no idea about). The heatpump, which was working fine now sounds like its struggling. Do the condensers need topping up like the air conditioning on a car?

The heatpump is covered by a service contract so I am not too worried by that, but the hotwater flow fault is a concern as no one seems to really know what's wrong. The diverter valve (which apparently cause problems) is now new. The solenoid valve (was supposed to be new) I don't think is working correctly, but I am also not conviced is the issue as that was bypassed with some flexi-pipe and the fault still showed up. Can a blockage in the hotwater coil occur?

The solenoid valve (was supposed to be new) I don't think is working correctly, but I am also not conviced is the issue as that was bypassed with some flexi-pipe and the fault still showed up. Can a blockage in the hotwater coil occur?

Yes but should be easy for a plumber to check. Basically jury rig something to get water to flow through the coil.

Might be as simple as energising both the diverter and solenoid valves to the right position then opening both drain and fill valves.

The symptoms do sound unfortunately like ours :-(

The water pump in the altherma ASHP is 'load compensated' which means it runs faster or slower depending whether the heat that the ashp generates is being fully consumed by the house.

So if the ashp fails to generate very much heat, the water pump will slow right down to match it, and this can register as a 'low water flow' fault code, despite being absolutely nothing to do with the water circuit.

In our case, the indoor refrigerant circuit gradually failed, so the heat was only what the outdoor unit could produce (about 35-45degC). This registered as a 'low water flow' fault as explained above, leading to fruitless water plumbing repairs, until Daikin pointed the installers to check the indoor refrigerant circuit.

The fault only showed up when the weather compensation controller called for a temperature much greater than 35degC. What temperature does your central heating run at in winter?

Yes, mine was the same. Through the summer the weather compensation ran it at 30 DegC and it didn't matter that the indoor unit wasn't boosting it. In the winter it tried to run hotter and that's when the fault became visible.

You could turn it off auto as an experiment and set the heating temperature to run at the same temperature as the hot water? That would show you whether the fault is only located in the hot water tank circuit, or is more to do with the ashp trying to run at high temperatures.