10mm microbore for expansion vessel?

[newshound]

Shouldn't be a problem, if you can find all the suitable adaptors.

But the expansion vessel can go anywhere on the supply or return pipework to the radiators. There's a lot to be said for fitting them on a flexible connection (like the filling loop). One thing I would recommend is fitting a ball valve for isolation, so that you can test and when necessary recharge the vessel easily without depressurising the main system. (You should fit a drain point downstream too, otherwise you will have to release pressure by cracking a compression fitting). And obviously, remember to de-isolate afterwards.

[newshound]

But as I said, you don't need to be that close to the boiler. External vessels usually hang on a bracket to keep the weight off the pipework. Having a flexible hose makes it easier to connect. Mine is tucked up quite close to the boiler so there is not much room around the Schraeder valve. By unhooking it, it becomes easy to attach a pressure gauge or a hose from a bicycle pump. Also, if I do want to depressurise it to check the pressure, by unhooking it from the bracket and swinging it out from the wall it is easier to direct the drain valve outlet into a suitable bucket.

I'm not sure what type of rubber is used in these hoses but I've never had one fail. They are mechanically well protected by the mesh which stops them getting kinked; a common failure mechanism for rubber is attack from UV or ozone which is always worse at stressed regions. And a dead leg like this (or a filling loop) will never get very warm from the water side even if it goes into the boiler outlet pipe.

[newshound]

There's no continous flow. You could use the type of 2mm or so OD capilliary tube used for some types of thermometer or thermostat!

[Stephen]

Hello,

I want to add an external expansion vessel to my combi boiler as I think the built-in one has failed. The built-in one is fed off a 15mm port on the DHW exchanger. I think it will be difficult to run 15mm copper to this, so could I use a short length of 10mm or will the reduced diameter cause problems?

Thanks in advance!

[Stephen]

Thank you. What is the advantage of using a flexible hose? I assumed this would perish over time due to the heat? I thought most boiler manufacturers specified copper only within a metre of the boiler? Thanks again!

[Stephen]

Thank you, that's reassuring. So if the 10mm microbore is not too narrow, I assume I can also use a "standard" isolating valve and don't need to use a full bore one.

What is the advantage of using a flexible hose? I was thinking the heat might make it perish and leak? I thought boiler manufacturers usually recommend copper pipes only within a metre of the boiler?