Central Heating Leading to Divorce!!!!

[Norcon]

The problem is that the pump will only run when there is a delivery of 70° water to the deposit.

At the take off port (from the accumulator) to the ufh the temperature should stay above 50c.

So when below, the heating pumps (ufh and radiators) are interlocked until the accumulator is up to temperature.
A strategically placed control thermostat takes care of this.
If the boiler is correctly sized then the accumulator will not be depleted of energy whilst the radiator and ufh circuits are operational.

Try lowering the control stat down to 50c and see what happens.

the range was hand built by a local company

Do they have a website? A link maybe?

 

[portugal99]

Keeping the exit from the accumulator at a fixed temperature is the problem...

Once the ufh pump is running the heated water is depleted... Why? because there is no hot water delivered into the accumulator whilst the ufh pump is running. (I have found a way of keeping the pump running, all the time if necessary)

As soon as the thermostat on the accumulator is below, say 50 degrees then the ufh pump stops and has to wait for the temperature to rise in the accumulator.

I am unsure what you mean by interlocked heating pumps until the accumulator is up to temperature?

Does the size of accumulator have any bearing on the process? If the accumulator was halved in size would there be any effect on the heating?

Even when the temp gauge on the accumulator is showing 50° the water moving into the ufh is cooling off. The outlet for the ufh is about mid way on the accumulator and the temp gauge is at the top if that makes any difference?

 

[Norcon]

I am unsure what you mean by interlocked heating pumps until the accumulator is up to temperature?

Preventing them from running as its pointless pumping cold water around a heating system.

Does the size of accumulator have any bearing on the process? If the accumulator was halved in size would there be any effect on the heating?

The accumulator will store excess energy and with solid fuel, particulary logs combined with say a fan assisted log batch boiler it can allow the wood to be burned more efficiently.

Copied from the Kuenzel site.....

German law (BlmSchV) requires a minimum capacity of 25 litres per kW of boiler output. However, this is not enough for a pure wood-fired heating system. We recommend a buffer storage tank capacity of 50 to 70 litres per kW boiler output if the system is based purely on wood and not combined with an oil- or gas-fired heating.

Even when the temp gauge on the accumulator is showing 50° the water moving into the ufh is cooling off. The outlet for the ufh is about mid way on the accumulator and the temp gauge is at the top if that makes any difference?

50c at the top will likely mean 40c or less at the ufh output.
Subject to just how much mixing is taking place inside the accumulator.

say 50 degrees then the ufh pump stops and has to wait for the temperature to rise in the accumulator

At a guess I would say the boiler is undersized but not knowing anything about the boiler (and what the manufacturer recommends) and pipework arrangement between boiler and accumulator, could be other things.
Where does the pump on the left of the image pump from and where too?