Voltage on Central Heating Pipes

[Silverpenny]

I've noticed there is a small (45V AC or so to earth) voltage on the pipes feeding my central heating radiators around the house.
I'm guessing this is just pick up but I'd like to get rid of it. Where should I bond the pipework to earth (as apparently it isnt currently)? My boiler is in the kitchen.
(For info: The voltage remains if I switch off the power to my boiler controls, no electric immersion installed)

 

[luminaire]

Bonding will go from your mains water stop cock and within 600mm of your gas meter (assuming you have GCH) to your MET (main earth terminal).
What type of supply do you have? Can you send in a pic of the supply intake?

 

[gas4you]

Bonding will go from your mains water stop cock and within 600mm of your gas meter (assuming you have GCH) to your MET (main earth terminal).

And before the first tee in the gas pipe work

 

[Softus]

If you have no plastic pipework anywhere, you could just bond the pipework that's most practicable and least unsightly.

However, since it's possible (in theory) to plumb an entire heating system with no metal-to-metal contact at rad valves, one point of bonding could be dangerously insufficient, so it would be wise to bond in the places where the risk is significant, for example chromed towel warmer in the bathroom, rad in utility room, etc.