HW not CH to Bathroom radiator?

[Vass]

Can I use the HW in my bathroom radiator rather than the CH ? I'd like warm towels all year round of is the only option to fit an electric rad ?

[Vass]

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[Set Square]

You haven't told us enough your system to be able to give a proper answer.

If you have an oldish gravity HW and pumped CH system, you could connect the bathroom radiator into the HW circuit and it would get hot whenever the boiler was running.

If you have a more efficient fully pumped S-Plan or Y-Plan system - with zone valve(s) and a cylinder stat - putting the bathroom rad in the HW circuit is not very clever because it will only get hot when the HW is actually being heated - which isn't very often.

In this case, you would do better to connect it after the pump but before the zone valves. That way, it would get hot whenever the boiler is running - either for HW or CH or both.

[Andy Hall]

Well you *could*. The problem would be that the radiator would corrode rather quickly.

Apart from the electric suggestion, there are three ways to do this from the heating.

1) Use the bathroom radiator as a bypass for the boiler. If you look at your system, you may find a pipe between the flow and return from/to the boiler before the motorised valve(s) with something like a radiator lockshield valve on it. The purpose of this is so that if the CH and HW thermostats are satisfied and the boiler is in full burn, there is a path so that the pump can continue to run and dissipate the heat. You could take this out and replace it with the connections to the radiator. 2) If there is no bypass, then connect the radiator to the equivalent positions - i.e. after the pump but before the motorised valve(s).

Either 1) or 2) will heat the bathroom radiator when either the CH or the HW comes on. It won't when neither is on.

3) Create a separate heating zone. This would need for the system to be changed to using an S plan configuration - one motorised valve for HW, one for existing CH and one for bathroom. (see Honeywell content site for info on this). This would allow completely separate control for the bathroom but would mean that a suitable thermostat for a bathroom would be needed.

[Mark Hewitt]

This is how my towel rail is configured and I wish it wasn't! When it pumps through the towel when all other rads are off it makes quite a noise and stops me from sleeping at night.

[Andy Hall]

You may be able to alleviate this by changing the pump to a Grundfos Alpha.

These automatically back off their power as the flow resistance increases, which I suspect here is the reason for the noise.

[Set Square]

Is there any danger of them backing off so much that there's insufficient flow to cool the boiler during pump over-run conditions?

[John Stumbles]

Or turning the existing pump down, as long as it still gives satisfactory circulation at a lower setting.

Yes, I have heard that caveat (though I haven't come across that situation in practice, but then I've come across vanishingly few Alphas)

[Andy Hall]

There is a control to set the operating speed/power.

In any case, though, there is not a need for a very great flow for bypass purposes - only enough to stop the water boiling if it were to otherwise stop flowing. Also, remember that this is more of an issue with cast iron boilers than those with low mass heat exchangers

[Set Square]

Yes, I wonder how well they work with automatic by-pass valves. AIUI, an automatic by-pass only opens on the pressure rise resulting from low flow through the rads when all the TRVs are closed. If the Alpha backs off so that the pressure *doesn't* rise, the by-pass may not open and the boiler may overheat.

[Andy Hall]

You just make sure that the pump is set at a point that it always overcomes the ABV.

[Set Square]

I probably need to educate myself about Alpha pumps. How many parameters can you change on them?

As we known, a conventional pump operates on a curve (per speed setting) whose two ends are at max pressure/zero flow and max flow/zero pressure. In a heating system with TRVs, it would seem to be desirable to have a pump which provided a constant pressure regardless of flow. Then, when one or more TRVs closed, the flow through the remaining radiators would be unaffected. I presume that an Alpha goes some way - but not all the way - towards this, so that there is still *some* pressure rise to open the ABV when all the TRVs close?

[Andy Hall]

This one just has one knob to turn for the setting.

If you look on their web site there is a procedure for setting the pump and ABVs.

There is a more sophisticated one - UPE 15-60, which has a choice of two modes of automatic operation plus a head control. You can have a remote for it if you want....

[Ed Sirett]

If you put it through one of those ladder type towel warmers they are made of copper or brass I think.

This idea is not new. Some of the 1930s mansion flats with central heating (in the very original and precise use of the term), put the DHW through the towel warmer. I discovered this when trying to change a washer on a basin tap. Only some of the flow to the bath & basin went through the towel warmer.

The OP will also introduce a substantial delay to HW arriving at the taps.

[Andy Hall]

Hmmm.... I can't imagine that this would be very good though. THe volume of water in the rail is not going to be large, and if it's just a basinful of water, the towels are not going to get very warm during ablutions. Running a bath would mean heat being supplied for a bit longer.

I suppose another variant would be to put the towel warmer across the cylinder coil. At least that would heat the towel rail while the cylinder is recovering from delivering the bath water.

[Roger]

The message from Andy Hall contains these words:

Boiling is not really an issue for me. Firing the overheat cutout is. I don't have an Alpha but I occasionally get the boiler isolated by the overheat stat which could be a problem if it ever happened when I was away from home in the depths of winter. However AFAICT it only happens when the boiler is heating the DHW shortly after the central heating has turned itself down for the night and then only so occasionally that I can't be bothered to bugger about with the flow rates though the heating coil and the automatic bypass.