Pressure in electric towel warmer

GT1 · Feb 17, 2012

Whilst working in clients bathroom today noticed small leak on towel warmer. It's a large chrome wall-mounted one with a 250watt element.

I had to take it off the wall anyway to do my job so once it was back on I tightened the bottom fitting where leak was. Assuming it had lost water from the leak I went to open the top fitting was where the bleed valve is so it could be topped up.
I then found that there was a MASSIVE amount of pressure in it..!!
And mean loads...

So a quick question to anyone that knows about such things.
should it have that amount of pressure... ?
Should it have plain water in there or something else..?
I could understand an amount of pressure in there due to normal expansion. However, the rad was virtually full. So very little air in there to expand.

I've left the client with instructions to bleed it every now and then for now while I research was going on with it..!!

Darkwood · Feb 17, 2012

To my knowledge you can have 2 different types of electric radiator / towel heaters ...

-oil filled
-water filled

i think you've got your physics a muddle hear if you heat water up it will build up pressure and water will expand there is usually up to 2" air pocket at top to allow for this expansion, some radiators are bought pre-filled with oil or water some are filled on install, when hot it will be like a car radiator cap i.e. you dont wanna open the valve as you could get badly scolded so suggesting to a customer to do this is dangerous advice, the air gap as you suggest should be bigger at top (approx 2" when cold) but check with manufacturers first this will allow adequate expansion and normal tap water is usually used.

GT1 · Feb 17, 2012

No I'm aware the water will expand. But the air trapped inside will also be subjected to warming (due to being inside a warm radiator and thus will expand also. The air, being a gas will obviously expand much more than the water. So releasing the pressure will be no more dangerous than bleeding a "normal" radiator, in fact less so, due to the lower temperature of towel warmer.
Will go with the fact that expansion is acceptable. I suspect that the rad was overfilled in the first place and left no room for the expansion, thus the high pressure I witnessed.
(the rad was cold when i cracked it open by the way)

Marvo · Feb 17, 2012

As far as I've experienced oil and water filled heaters aren't under any pressure when cold. One thing that comes to mind is that I would remove the element and check to see if the outer tube is split. If the oil or water came into contact with the inner heater wire of an element then electrolysis would occur and this could cause high internal pressure.

If it's water filled then you would see the fault with a standard IR test @ 500 or 1000 volts. If it's oil filled you probably won't see it during testing, only with a visual inspection.

JD6400 · Feb 17, 2012

The element will last longer if you put inhibitor in as well , or so i have been told .

HandySparks · Feb 17, 2012

The pressure might well have been caused by the gasses produced by corrosion. As dp says, if it's just plain water at present, a small quantity of inhibitor would seem to be a good idea.

If it's not corrosion, then just bleed when pressure is high and leave it. If it's a standard tubular towel rad, it won't matter if the pressure goes below atmospheric on cooling. Don't fill to the brim unless manufacturer's instructions say so.