Pumps to run or not to run?

Hi,
Could someone tell me this?
When there is heating demand from external controls, should the primary circulation pump to the boiler run in conjunction with the heating circulation pump?
My store has demand to the boiler but as soon as the store gets above 60 c according to ACB display. The power to the primary pump drops to only 167v and then the heating pump kicks in at 240v. This is causing the boiler to overheat because there is no longer circulation on the primary pump. When the store temp drops to below 60the power to the heating pump stops and the primary pump gets 240v and starts circulation again. I'm getting intermittent heating. Surly the primary pump should continue throughout the heating demand? Is this faul atributable tithe ACB or something else. I'm getting no error codes on the display.
Cheers guys.

I personally suspect that your PCB is faulty because boiler pump shouldn't have less than 240V. If it is less when another pump starts then most likely control voltage for boiler pump drops(or modulated because of internal PSU voltage drop) under another load. Either try to replace or repair it.
By the way, if store temp drops below 60 then it is normal that heating pump stops.

Thanks for reply,
I'm suspecting the ACB at fault too, because they cost so much I don't want to overlook any thing more obvious. I have read the manual for this unit, I have to say its not very comprehensive. Shame there is no functional flow diagram like with most good boilers. Do you have any experience of repairing the pcb ACB? Like what components to look at. I have heard a buzz from the ACB on occasion so could be a dodgy relay or bad connection I suppose?
Thanks

There is no relay on this board as far as I remember. The buzz is usually normal, coils do it. It is difficult to say what is faulty on the board without some measurements. The simplest and cheapest you can do is replacing few caps but I'm not sure if it will help in this situation, check my posts. Otherwise I can't help much, you need to be good in electronics to go further.