Hot water really hot and bathroom radiator randomly coming on

[UndercoverCop]

Yesterday morning I noticed our bathroom radiator was on, the heating thermostat was set to 16 and showing an internal temperature of 24, no other radiators were on. The hot water was on (old cylinder type system) radiator is not plumbed to the hot water because it's never done it before, bathroom was refitted and radiator installed about 18 months/two years ago.
Today I've noticed the hot water coming from any tap is really hot are the two things linked? What is it likely to be? Do we need an emergency bank holiday weekend plumber or is this ok to wait until next week?
@pigletjohn and others, any ideas?

Hi not sure about what may be wrong here but I do know that our bathroom radiators do come on with hot water when the heating is not on. We like it actually as it drys the towels when we don't want to hat the house. Could it be that the thermostat on your hot water tank is too high and hot water overflowing into heating system.

I'm not an expert but I do know of a very kind and knowledgable MNetter who is usually happy to help with plumbing questions @pigletjohn

Sorry I should have read your full post 🙈

Are you using an electric immersion heater?

How old is your gas boiler?

Some photos of the cylinder, and the pipes, cables and switches around it, would be helpful.

We have three towel radiators, all of them have two tap like fixtures on them. We tried turning these, first one way, then the other. Wouldn't turn off. Ended up turning them off at the wall switch. Then they were still on, so we unscrewed a panel and took a fuse out, still on. I can't remember how we turned the bloody things off in the end. I think a plumber came for something else and knew which way each of the taps needing turning, maybe.

Turns out they operate on both oil OR electricity. We didn't have any oil at the time! They were also costing 10 kWh each in electricity to run.

They were on when the heating was not, so yes they are connected to the hot water.

My LL mostly employed cowboys to build this house, I don't suppose that's the way towel radiators are meant to work, but I am sure piglet John can confirm.

The tap temp will be down to the temp it is set on the hot water thermostat, that can be turned down.

I also notice ours gets far too hot if we don't use all the hot water in a day, or if the house has got particularly hot (probably the loft) so I guess the pipes get hotter?

No I don't think you need an emergency plumber.

If you are lucky enough to have a hot water cylinder close to the bathroom, heated by a gas boiler, it is possible to plumb the bathroom radiator ot towel rail so it warms when the cylinder is being heated (typically during and after a bath or shower). This is a very superior design. Solid fuel or wood boilers are often plumbed that way to prevent overheating.

It can also be caused by faults, such as a worn-out motorised valve or incorrect installation.

I expect we'll be able to puzzle out the cause by looking at some pics.

Sorry been out today. I spoke to the person who fitted our bathroom and the rad is definitely not running off the hot water. It is the first on the system though after the tank. We do have a gas fired boiler and a cylinder tank right next to the bathroom, it's in a big airing cupboard in the back bedroom.
It's not letting me upload images for some reason it says the files are too big but they're just basic pictures.
There is a small white thermostat on the cylinder set to 55, there are two motorised diverter valves.
I did give this evening that our actual boiler had been turned up to between 4 and 5 so I've turned it down and will see what happens in the morning when the hot water kicks in. By the time I found it the evening got water time had been and gone (4:30-5:30 so DS has water for his bath)
I will keep trying to upload pictures

What colour is the cylinder?

Are you using an electric immersion heater?

Can you see a motorised valve like any of these?

https://www.screwfix.com/search?search=Port+valve&price_from=50&price_to=125.0

Oh yes, I see you have.

As you have two, I expect they each have two pipes connected ( not three pipes).

One probably feeds the cylinder and gets hot while the cylinder is being heated

One probably feeds all the radiators and SHOULD be cold when the CH is off (all summer)

If the cylinder stat and valve are working, it should not matter if the boiler is a bit hot, unless the stat is too near the bottom of the cylinder. Condensing boilers reach peak efficiency around 60C.

No electric immersion heater, cylinder is a yellow/cream colour, boiler is older than we've lived here which is about 6 years and wasn't brand new when we moved in.
The thermostat is right near the bottom of the cylinder
The motorised valves both have a little lever type thing on top, one slides across when the hot water is on the other when the heating is on.

It's really annoying I can't upload pictures. Keeps saying they are more than 6mb but they're not

The valves on your link are almost identical to the ones we have

Feel the valves when the boiler is running. The one that has a pipe to the cylinder should get hot, the one that only feeds the radiators should stay cold.

Observe that two pipes from the boiler go into the side of the cylinder. One near the bottom and one a foot or so higher. These heat the internal heat exchanger coil. How high are they, and how high is the cylinder stat? It should be higher than the lower pipe.

What are the dimensions of the cylinder? Is it easily able to fill a bath, or does the hot water start to run cool?

I don't remember how old a yellow cylinder is, but I think it is more than 30 years. It is not as efficient or as well-insulated as a modern cylinder.

You might be able to edit your picture files to reduce their size, but I don't know how.

So I manually turned the heating valve on and off again yesterday using the little black lever, since doing that and turning the boiler down a bit we seem to be back to normal.
We live in a high limescale area and the heating had been off since April until last week when it kept raining and I just couldn't get a load of already wet washing dry. I put the heating on for an hour just to get it going on airers. I'm hoping there was just a bit of limescale or something blocking the valve from fully closing.
Fingers crossed

With age, they wear out. Does it get hot when the heating is "off?"

20 years is typical but it varies a lot.

Summer is the best time for heating repairs.

@PigletJohn so it doesn't seem to be happening anymore, but I've also not used the heating since. I also remembered both motorised valves were replaced about 2/3 years ago