Combi boiler needs topped up regularly - faulty pipework?

[alan333]

Hi,
2 bed upper flat had a new combi boiler installed 10-15 years ago (there was no existing system). Radiators are piped under the floors in grey plastic pipe, bigger than microbore - maybe 15mm pipe (will check tomorrow). The boiler always used to lose pressure and the fill loop was used regularly to top it back up. No leaks have ever been found. A new Worcester Bosch Greenstar CDi Classic was fitted April 2014, using the same radiator pipework, and I've recently found out the heating still loses pressure. Plumber reckons the grey plastic pipe is somehow allowing pressure to escape.
BTW it's a friend's rental property so I'm only in it occasionally, and it has 5 rads with trv's and a towel rail with a standard valve. The boiler is serviced annually, most recent Nov 2017.
Also, the most recent service says there is "no cross bonding at boiler" and "no cross bonding at (unreadable, maybe mouth, or motor, or master - I suppose it could be meter but it really doesn't look like it?) - I'm thinking this means there's an earth connection to some pipe somewhere but not between all the pipes. Again, I'll look tomorrow.
Any thoughts?
Regards
Alan

 

[endecotp]

the most recent service says there is "no cross bonding at boiler" and "no cross bonding at (unreadable, maybe mouth, or motor, or master - I suppose it could be meter but it really doesn't look like it?) - I'm thinking this means there's an earth connection to some pipe somewhere but not between all the pipes.

If you'd like to ask about this in the Electrics forum you'll get a lovely 18-page thread....

Bonding plastic pipes - or short lengths of copper pipe that connect to plastic pipe - is obviously pointless.
Even if the pipes were all copper it would still not need bonding. Plumbers like to do this though; I don't know why.

The lack of bonding at the meter may be because it's a flat. AIUI, what's essential is bonding where any metal gas or water pipe comes up out of the ground. Bonding at the individual (upper) flats is commonly done, but I don't know if it is a strict requirement.

 

[alan333]

Thanks mate, I'll have a look today.

 

[alan333]

Had a look today. It's piped in 15mm grey plastic pipe right enough, and there are no earth wires visible anywhere to the boiler pipes. One of the Drayton TRVs is on the return side - would this cause problems?

 

[endecotp]

Had a look today. It's piped in 15mm grey plastic pipe right enough, and there are no earth wires visible anywhere to the boiler pipes.

That's as it should be.

One of the Drayton TRVs is on the return side - would this cause problems?

Some valves are bidirectional, others aren't. It may have arrows on the valve body.
If it's working correctly and not making odd noises, it's OK.

 

[alan333]

Could the trv being on the return side cause anything to do with the system losing pressure?

 

[endecotp]

I can't imagine how that could cause it to lose pressure.

 

[alan333]

Thanks again

 

[John D v2.0]

Bonding is neede between the main earth terminal (which will be either in or near to the consumer unit, or on the meter board) and the incoming metallic parts or the gas pipe in your case. Gas regs only allow it after the meter, and electrics regs require it where it enters the flat.
Your water only needs it if it's not plastic where it enters.