i have main fuse keep blowing on my central heating system could this be the pump ?...ive changed the acuator and Stat ! but it keeps on blowing the main 5amp fuse (in the fuse box)after 5 minutes after switching on ! any ideas !...the pump feels cold when the heating system fuses after being on for 5 mins ! ..so can the pump still fuse the electrics even after 5 mins /?