Just a couple of things I'm curious about

[Gary0]

No great need to know, but have been wondering about them both for a while.

I've been informed that one should not bleed radiators that are supplied by a combi. I can not claim that the guy who installed the system in my place mentioned it, so I wondered a) if it were true, and b) if so, why is that, since bleeding radiators seems to be a common first check when one has problems.

It sometimes seems to be the case that the radiator in the bathroom is not fitted with any control knob, and so has to be permanently on. I wondered why this is, since, if there was some need that I am unaware of to have a permanent flow, surely someone could loop a pipe somewhere without feeding a radiator ?

Just curious, thanks.

 

[ChrisR]

a) bullox

b) You have to refill with water if you've bled air out. Systems which need bleeding after installation air settlement, have corrosion problems though.



"if there was some need that I am unaware of to have a permanent flow"
There is with some boilers so they can control themselves. No water flow means thermostats indide the boiler might not get hot. This is more often the real need than more the widely accepted one, that the boiler may have to lose excess heat so needs somewhere to dump it if all the valves are shut. This can be a large need too though!

You can usually fit the loop of pipe you mention, instead, with a Bypass valve on it.

 

[chrishutt]

bleeding radiators seems to be a common first check when one has problems.

Far too common. The only reason to bleed a radiator is to release air trapped in it. If there is air, the top of the radiator will remain cool when the bottom is hot. Otherwise there is no reason to vent.

The above applies equally to sealed (combi) systems and open vented systems. But in the case of the sealed system, you need to check and, if necessary, restore the pressure after venting.

Bathroom rads are often left permanently on, mainly to act as a by-pass but also because bathroom rads often act as towel rails, so heat output is reduced, and the rads are small. Normal thermostatic control would then be pointless.

 

[Gary0]

Thanks both.

Have to say that in a small bathroom, one can accidently get uncomfortably near a hot radiator on occassion

But that's cleared both points. And well worth emphasising checking the pressure should there ever be a need to bleed.