Multi fueled radiator?

[tj]

Hi

I have bought a bathroom radiator which connects to a regular central heating system, but that can also operate on electric alone.

In the documentation it says, when using radiator in electric mode, never close the return valve.

It is intended to be used purely on electric for the time being and at a later stage connected to a central heating system, so in the shop I asked if it was ok not to be connected to a system and run just as an electric radiator? they said yes that was ok, just fill it with water.

Having thought about it and the reference to the return valve, should I actually pipe the inlet and return together? I suppose my real question is why should the return valve never be closed? is it to allow for expansion?

any help advice appreciated

 

[Gluestick]

When the rad is connected to your central heating system, it will be pressurised to above atmospheric, as French systems (like combi systems) have static pressure.

If you isolate any radiator in the system (by turning off both valves), then the pressure should remain,  until it gradually "Bleeds" off, mainly owing to natural leakage from the rad valve seals, over time.

One can only presume that the recommendation to "leave the return valve open" has to relate to natural expansion. The heating element inserts usually have a thermostat, which would limit the maximum temp, thus excess expansion should not actually be a problem. Neither should pressure, since the rad should not reach anything like boiling point, as the thermostat will limit the maximum temp atg well beneath 100 Deg. C.

The total expansion (by volume) is circa 4.3% from freezing to boiling - bearing in mind that water actually expands between the mid point and freezing and boiling! i.e. it occupies the least volume above freezing and below boiling. Complicated, huh? Thus probable expansion between ambient (room) temp and top operating temp would be in the region of 2-3% only by volume.

Probably, what I would do is to fit one pipe, only, to the return valve and make this an expansion pipe: run it upwards and fit a bleed-off valve and half-fill this standpipe, to ensure the rad is full, to bleed off air and to allow expansion into the pipe. Then all you will be doing is compressing the standing air.

BTW: don't forget to add anti-corrosion fluid, when you fill the rad!

I can see no benefit or reason to join both outlets with a looped connection.

 

[tj]

[quote user="Gluestick"]

Probably, what I would do is to fit one pipe, only, to the return valve and make this an expansion pipe: run it upwards and fit a bleed-off valve and half-fill this standpipe, to ensure the rad is full, to bleed off air and to allow expansion into the pipe. Then all you will be doing is compressing the standing air.

[/quote]

Was with you right til this bit :)

Would'nt the pipe always be full since the rad is 1.5 metres tall ?

So is the point then to leave a little space for expansion? if so cannot I simply put a stop where the return valve should be, a bleed stop on top and a filler / drain plug on the inlet,  fill it up and leave a little air in it?

 

 

[Gluestick]

I would make the standpipe, taller than the rad.

Easier to fill the pipe than the rad.

Personally, I would not leave airspace in the rad, per se, as this, with heat, can encourage corrosion: basis, Heat + Air + Mild Steel = Iron Oxide, plus a series of elementary salts from the various chemical compounds in the water, such as chlorides, sulphates, nitrates etc.

Plus, of course, the rad would "Chuckle" as it warmed up. The same aspect applied to the standpipe, would be Heat + Air + Copper, which would corrode less than Mild Steel. Plus the pipe is only temporary and can be junked, when you finally install the heating.

Just me, being pedantic I suppose! [:)]

Theoretically, I cannot see that expansion would be too much, actually, as the temp is restricted by the 'stat.

Suck it and see?

 

[tj]

Hi

Thanks for your very knowledgable reply,

What about a compromise? since a pipe taller than the rad ( 1.5 m) would look out of place, a short length of pipe, say 10 - 15 cm, from the top of the rad with a bleed stop, so when its full I could drain off a little water so the pipe would have air in it and not the rad?

cheers 

[Michael]

  tj. I would not use the rad until you have connected up the heating pipework, the reason why the return valve must not be turned off is so to allow for safety expansion into the heating system when the heater is on, and if the stat on the heater breaks down it could be like blocking the spout and lid of a kettle ,could in practise cause a bit of bother..Michael.

[Gluestick]

Strange: Screwfix offers heated towel radiator electrical heating inserts and states, "Use with plumbed or non-plumbed......................."

As I stated before, the total expected expansion of water would be max. 4.3% from freezing to boiling.

If the stat did fail, and the element continued to supply heat, then eventually, probably the water may well boil and this would blow-off the valve seals and/or the standpipe bleed and/or the solder joint.

If all the water was evacuated, as steam, then the element would quickly over-heat and either the Fail-Safe internal fuse would blow: or the element would rapidly burn out, or trip out the MCB.

If one was really worried, then fit a safety valve on the standpipe!

However, in practice, the built-in safety device would cut out, before the boiling point was reached and the heating coil and stat would have to be replaced. Double Level Redundancy, i.e.

All modern heating elements (immersion, kettle, electric rads, coffee makers etc), have some form of over-heat protection. Years ago used to be a fusible link - soft solder; it would simply melt!

These days, tends to be a thermister, heat sensitive fuse, heat dependant resistor etc. All good quality approved electrical mains equipment has such safety features built in, even power supply transformers.

If you Google "Immersion Heater Elements Safety" you will see what I mean...............

 

[tj]

Hi

Lots of information on the safety angles,

So do you think the short pipe from the top would be sufficient?

thanks

[Gluestick]

Provided it sits slightly above the topmost rad level, yes.

Just allow a little pipe above the rad's upper position, for the air gap.

Bonne courage !

 

[Bassman]

I bought one in Brico Depot recently which as far as I can see is purely electric (towel rail type) and this came with a plug in the top and a seperate air bleed valve to replace it with once installed it was also ready filled with anti corrosion stuff [:)]

[Gluestick]

If I was going to install a rad purely to be heated by electricity, then I would probably make sure all the seals would not be affected: and fill it with light oil!

Would take an awful long to corrode, then! Oil-filled rads and heaters, are of course quite common, of course.

Like your new descriptor, Paul ![:D] Self-awarded?