2 radiators on with hot water only

[Batman63]

Can anybody let me know if they've experienced 2 radiators gettng warm upstairs (both above the boiler) when the boiler is only set to hot water. It's a four bed house and the other 4 rads upstairs don't get warm so I'm guessing not divertor valve related which is only a couple of years old. I can turn the two hit rads off with the TRV's but never noticed before so it may have always been like it.

 

[SJB060685]

What you're experiencing can be described as thermal drift. This is caused when the returns from cylinder and central heating are plumbed up wrong, resulting in hotter, less dense water rising back up the return of central heating when the hot water is on, displacing the colder and more dense water as it goes and some of the rads start to feel hot.
A non return valve might prevent this, also re piping the returns into the common return so the hot water is last tee into it closest at the boiler.

 

[Batman63]

What you're experiencing can be described as thermal drift. This is caused when the returns from cylinder and central heating are plumbed up wrong, resulting in hotter, less dense water rising back up the return of central heating when the hot water is on, displacing the colder and more dense water as it goes and some of the rads start to feel hot.
A non return valve might prevent this, also re piping the returns into the common return so the hot water is last tee into it closest at the boiler.

Many thanks at least there's no initial problem as it's probably been like it since 2004 when the house was built and I've only owned the property for a couple of years. I've always noticed the rad in the ensuite got warm on hot water only so I'm guessing the one in the bathroom has always got warm but gone unnoticed

 

[SJB060685]

The problem is common when a plumbing rule if you will is not followed. If it is that that's the cause its of no real problem and can easily be rectified.
To be sure its not a motorised valve partly letting by you can place your hand on the CH flow after the valve, as far as you can and see if you can feel heat.
Also its not uncommon to have a towel rail, or radiator in a bathroom/ensuite piped off the HW circuit, so that radiator might be piped like that.

 

[Batman63]

The problem is common when a plumbing rule if you will is not followed. If it is that that's the cause its of no real problem and can easily be rectified.
To be sure its not a motorised valve partly letting by you can place your hand on the CH flow after the valve, as far as you can and see if you can feel heat.
Also its not uncommon to have a towel rail, or radiator in a bathroom/ensuite piped off the HW circuit, so that radiator might be piped like that.

Many thanks for your advice. I've just checked an the CH flow is not getting warm with the hot water on so I'm assuming as you've stated it's probably bad plumbing practice to make it easier for the plumber at the time.
I don't have any towel rails but the ensuite radiator and bathroom radiator are side by side and both sit above the boiler which is below in the utility room

 

[SJB060685]

The radiator/radiators most likely to be affected by thermal drift are the closest rads upstairs to where the two returns are. In this case as you've said I'd suspect them to be the two radiators you've mentioned, although i haven't seen the pipe runs.

 

[Batman63]

The radiator/radiators most likely to be affected by thermal drift are the closest rads upstairs to where the two returns are. In this case as you've said I'd suspect them to be the two radiators you've mentioned, although i haven't seen the pipe runs.

Thanks again much appreciated

 

[Murdoch]

As you mention the bathroom and en-suite this May be deliberate so your towels can dry.

our house is plumbed this way

 

[Batman63]

As you mention the bathroom and en-suite this May be deliberate so your towels can dry.

our house is plumbed this way

Ah that would make sense and in the summer they anticipate you will turn the TRV's off so the rad is cold when you want hot water

 

[moonlight]

Your assumption maybe correct. Before the hot water comes on next time. Feel the pipes near the valve. Turn the hot water on if you have a mid position valve the water comes in at the bottom and will leave on one side of the valve. If both sides get hot your valve is letting by.