problem with thermflow thermal store mains pressure system

[kennyspark]

Wired up this system in accordance with manufacturers wiring diagram. The system is heated by a gas boiler as main source of heat and has the option of using solid fuel to heat the cylinder also. On the cylinder there is a cylinder stat which is nominally set to 75 deg and this controls when the boiler and boiler pump are on .There is also a solid fuel stat on the cylinder which is recommended set at 90 deg. This has been wired as normally open so it should not switch on the central heating pump until this temp has been reached. System works on principal that you can have hot water by itself but when c/h is switched on then the hot water has to be on also. Danfoss programmer FP715si is used set to Gravity to switch on hot water and central heating.
The system seems to operate correctly initially. Boiler pump and boiler turn off when temp at cylinder reach 75 deg. The Central heating pump turns on and off when you switch the programmer c/h button on and off.
The problem I am having is that after the system has been running for approx. a day the c/h pump stays on even with the programmer turned off.
I have ruled out the solid fuel stat to be the problem by completely disconnecting it so the only supply to the heating pump is via the switched live from terminal 4 of the danfoss programmer. I have tried two programmers and tested continuity at the back terminals. When installed there is continuity between L and pins 1 and 2 as it should be and no continuity between L and pins 3 and 4. After testing the programmers after running for approx. 1 day there is continuity between L and pin 4 effectively shorting out the switched live.
Would appreciate suggestions to the cause of this. Both pumps are brand new grundfos types rated at max 1a so the programmer should quite easily handle both loads.

 

[Agile]

I presume that these are the new smart Grundfos pumps!

Look on the Grundfos Facebook page and read the explanation that I have posted there to help those like you!

Tony Glazier

 

[kennyspark]

Thanks for that information Tony. I wasn't aware of this and the heating system supplier wasn't either. The pumps are as you said Grundfos smart UPS2 types .