From buzzing to always pumping

Hi, we had the dreaded buzzing sound, and duly determined that it was the pcb board, and replaced it.

However, I have now put the old board back, as the new one made the pump keep going, pumping hot water rtound the rads, with the stat on the wall indicating 27 degrees, even when the stat was turned down to 19 and the boiler (I think) was off?

When I put the old board back, the pump returned to going on and off immediately the stat clicked either way respectively. For a while I thought the new board was doing the right thing and letting the hot water continue to pump for a while, but I think it turned out to be more like an hour before we realised it hadnt gone off and it was getting very hot. I'm guessing the new board could actually be ok and something else might need to be changed?

Any pointers gratefulyl recieved.
Jules

Hi Jules,

It'll be a faulty new board. I encountered this fault several times earlier this year. I think Gledhill probably made a bad batch. The CH pump should turn OFF as soon as the stat clicks when you turn it down.

Cheers, Mike