Boiler badly installed?

[merluzzo]

I have a combi boiler (Worcester/British Gas RD 542i) that I found in a house I bought in 2012.

Reading the manual I just realised that the filling loop is connected to the CH flow pipe instead of the CH return pipe (as the manual says it should).

I started investigating the boiler as there is a slow but constant loss of water pressure. Opening the filling loop makes the pressure gauge move quickly above 2 bars. Other than that, the boiler works, but hot water from the taps often becomes cold for a few seconds and then hot again.

Can the system still work OK with these weird connections? And can I connect an external expansion vessel to the CH flow pipe by teeing just after the non return valve?

[Mike4]

I have a combi boiler (Worcester/British Gas RD 542i) that I found in a house I bought in 2012.

Reading the manual I just realised that the filling loop is connected to the CH flow pipe instead of the CH return pipe (as the manual says it should).

I started investigating the boiler as there is a slow but constant loss of water pressure. Opening the filling loop makes the pressure gauge move quickly above 2 bars. Other than that, the boiler works, but hot water from the taps often becomes cold for a few seconds and then hot again.

Can the system still work OK with these weird connections? And can I connect an external expansion vessel to the CH flow pipe by teeing just after the non return valve?

Firstly, BG branded boilers are never quite the same as the boiler you think has simply been re-badged. There will be sensors missing, simpler PCBs, smaller heat exchangers and all manner of cheese-paring economies not obvious at first sight, so be careful of relying on the Worcester version of the manual. Secondly, the cold fill connection into the return pipe does not matter a jot.

The rapid loss of pressure tells us 1) the system is losing water and 2) the expansion vessel has probably lost its air charge. Pump it up again with a footpump! And yes you can connect an external vessel if you wish, connection location can be anywhere on the system and it will still work.

Fluctuating hot tap temp is usually water scale contamination of the domesrtic heat exchanger.

[merluzzo]

Thanks Mike, this is very useful. It makes sense that one can pump cold water at either end of the CH circuit with equal results.

I will try to pump air into the expansion vessel if I can access its valve (the boiler has been boxed in drywall and tiles and I don't feel confident in completely removing it from the wall).

I have checked all radiators and their valves and cannot find a leak. The 15 mm copper pipe that goes outside the house from the boiler does not seem to drip. My hope is on the expansion vessel at the moment.

Cheers,

Merluzzo

[Mike4]

Thanks Mike, this is very useful. It makes sense that one can pump cold water at either end of the CH circuit with equal results.

I will try to pump air into the expansion vessel if I can access its valve (the boiler has been boxed in drywall and tiles and I don't feel confident in completely removing it from the wall).

I have checked all radiators and their valves and cannot find a leak. The 15 mm copper pipe that goes outside the house from the boiler does not seem to drip. My hope is on the expansion vessel at the moment.

Cheers,

Merluzzo

Boxing around a boiler is the kiss of death for proper maintenance. This is prolly why the expansion vessel is flat - the air valve is usually around the back somewhere with access prevented by the boxing-in.

Fitting an additional one is a perfectly good fix - until the old flat one begins to leak!

Once you get some expansion capacity into the system, the period between raising the pressure may well rise from days to months.

[UncleEbenezer]

Fluctuating hot tap temp is usually water scale contamination of the domesrtic heat exchanger.

Is it?

I have the problem he describes (fluctuating when turned on, but more stable longer-term). I've encountered the phenomenon in various places. This one has quite a bad case of it, but is a soft water area: my kettle has had more than twenty years of several-times-a-day use without even a hint of scale.