Posted by: @suzer

We have towel rads in the bathrooms that are heated from the heat pump. They don’t get very warm unless the heat pump is at full tilt on a very cold day. Is that to be expected? We have under floor heating so not using to heat the room like in previous house that was on mega flow heated by gas. 

Pretty much, yes.  We have the same; a towel rail in the main bathroom.  Unless your ASHP is set up with a separate zone for the towel rails and you can vary the flow temp in that zone separately,  the towel rail won't get any hotter than the ufh.  That also means no heated towel rails at all when the heating is off. 

We had a separate electric old style radiator incorporating a towel rail installed.  Heats the bathroom nicely too.

Like this:

NWTDIRECT.CO.UK "https://nwtdirect.co.uk/traditional-electric-towel-rails/506-2637-635mm-x-1000mm-electric-tranmere-traditional-towel-rail.html#/63-electric_element-400w_single_heat_electric_element"

635mm(w) x 1000mm(h) Tranmere Traditional Electric Radiator

The Tranmere traditional electric towel rail is pre-filled with a glycol mix and supplied with a choice of electric element.

A radiator off the ASHP is never going to do the job.

They are dual fuel ones so could be run on electric.  Don’t need hot towels that badly 😂

Posted by: @suzer

They are dual fuel ones so could be run on electric.  Don’t need hot towels that badly 😂

Dual fuel with ASHP?  Not so much a case of requiring hot towels as dry towels that don’t smell musty because they aren’t dried quickly enough.  Also a nice warm bathroom which, fully tiled, is warm enough to prevent condensation running down the walls from even the quickest shower.

An interesting conversation. We have two towel rails connected to the central heating. Oddly enough, they are always hotter (significantly hotter) than any rads in the house, including the K3s. I use them as a metric to see whether the heat pump is working as it should. This may, however, just be our piping which isn't amazing, but I thought I'd share my two cents' worth.   

@suzer, we have a dual fuel one in the master bathroom. It was a hassle to get the electric connected to it, so we never did hook it up. In hindsight it may have been a good idea with the crazy electricity tariffs. 

Our towelrails have become pretty much useless after switching from Oil to ASHP.  They get tepid at best (our heating flow temp is 35 degrees).  I like Adam's suggestion of replacing them with electric.  I'll get a plumber to quote for that next time we need some other job doing...

@novemberromeo, we have one electric towel rail that we had to turn off because it consumed electricity like crazy. Have you had your rads balanced since moving to the heat pump because that could be an issue – would found that our rads were completely out of kilter when the ASHP went it, and when the rads were rebalanced, we had far better heat distribution.

Our towel rails are in the same circuit as the upstairs radiators, so only get warm when the heating is on, with one exception.  The ensuite in our master bedroom didn't have a towel rail at all when we moved in, so when we refitted it we had one put in.  The bathroom is right next to the hot water tank, and to make life easier for themselves the plumbers connected the towel rail to the nearest heating feed that they could get to, which happened to be the main feed from the boiler, before any of the 2-port valves to switch between heating and hot water, so the towel rail was always warm when the boiler was running.  

The plumbers who did our ASHP install didn't change it, so now it is warm whenever the ASHP is running, just gets a bit warmer when the water is heating! Also means that when the heating is off over the summer the towels still get dry when the hot water comes on.

A mistake that we're happy not to rectify!

My advice would be to have a towel rail only to hold a towel. Not heat it. Fit dedicated bathroom radiators to heat the bathroom which in turn will dry the towel hanging up elsewhere in the room. 

If you fit a heated towel rail, its designed to retain heat and dry a towel, not emit heat. Plus your towel blocks most of the surface area anyway. My bathroom is warmer with a dedicated bathroom radiator with a flow temp of 38 than when we had an oil boiler and a heated towel rail with a flow temp of 50-65 degrees. It was boiling to touch but didn't give off any heat. 

Electric towel radiators are terrible as they are costly to run, won't heat your bathroom and setting a timer to dry your towel at set time each day requires you to shower at the same time every single day unless you manually switch it on and off. 

I don't zone our bathrooms and just leave the TRVs on the highest setting so if any of the bedrooms call for heat upstairs the bathroom radiators will get some flow at the same time.

If your towel rail has an electric heating element, one solution is to fit a boost timer on it.  For example this one should be a drop-in replacement for a fused spur switch:

TIMEGUARD.COM "https://www.timeguard.com/products/time/immersion-and-general-purpose-timeswitches/4-hour-electronic-boost-timer-and-fused-spur"

(they also have a non-spur version with a larger button, and various display/wifi/etc versions)

When you've had a bath, you press the button once for 1/4 hour, twice for 1/2 hour, three times for 1 hour, etc.  It then shuts off after the appointed time.

You can get towel rails with both central heating water and electric elements - the central heating provides heat in the winter, and you just press the boost button when needed for electric heat in the spring/summer/autumn.