when the hot water system comes on line, the radiator in the bathroom becomes hot but the heating is not on..?

Answer 1

That's because the heating coils for hot water and central heating use the same burners. Notice in the winter how you always have hot water much quicker too?
When you run your hot water tap, you will hear your central heating pump and blower start up too.

I hasten to add that my boiler is only 2 months old and is a Vaillant, so I know it's not knackered.

Perfectly normal; don't worry.

Answer 2

Most radiators in bathrooms are connected to the domestic hot water side of the heating system so that when the water is heated by the boiler it heats the water in the radiator (which then get hot as you note) and also runs through a coil inside the hot water tank where it heats the water which comes out of your hot taps. The radiator should be on a branch so that if it is turned of by the radiator valves the water in the tank still gets hot - if it not on a branch you got problems because the hot water from the boiler has got nowhere to go and something could explode.

As for the blockage in the boiler answer earlier, I think he just turned off your radiator.

Answer 3

How do you people live? Good God, what kind of plumbers did work in your homes? The only type of bathroom "radiator" that should get hot with the water running is a heated towel rack. And it heats up only if the hot water in the shower is used. This only applies to those that work with the potable water supply. Some racks are electrically heated.

Some people, reading this haven't a clue about what is a heated towel rack.

If any radiators are heating when your boiler is running just to make hot water, then you need a flow control valve on the feed above the boiler. Hot water is being circulated in the system by gravity. Heated water rises, colder water returns to the boiler. How did you think hydronic systems worked before the advent of electricity and circulator pumps?

Answer 4

A lot of people seem very sure they can solve your problem without knowing the details of your system, they should all be plumbers !

It could be
1 - a fault ( unlikely )
2 - badly designed ( possible )
3 - correct ( possible )

If you have a cast iorn boiler ( like a range cooker or something ) then a lock shield valve should be installed as a bypass loop to allow hot water to circulate out of the boiler even if all the rads are off, its to stop the boiler overheating. Some/many/a few people put a small raditor in this loop to help disperse the heat.

Conduction transfers betwwen hot and heating systems in the boiler and convection can raise heat to the nearest radiator. Try turning off the rad in the bathroom and turn another upstairs one on - see if the heat transfers to this one.

Personally, id leave well alone and see whats in the fridge.

Answer 5

Oh my god !! I can't believe how many people don't know what they are talking about but still give answers... A thermocouple !! LOL

Anyways as a couple of people said, the bathroom rad in some houses is tied into the hot water circuit of the heating system, this is as said before to heat your bathroom or towels when the hot water is in demand.

On the other hand it could also be down to a faulty zone or 3-port valve. It could be passing hot water from the hot water circuit into the heating. But this is more likely if the problem has just started.

Oh and dont worry about explosions, I've never seen water explode! even old boilers have temperature devices fitted to stop anything dangerous happening.

Answer 6

the bathroom radiator is connected to the hot water pipes feeding the cylinder controled by a zone valve, the reason being is to use up the excess heat in the hot water system and keep you warm when in the bathroom when butt naked, it is known as a byepass radiator and it prevents the boiler thermostat from cutting of the burner to soon and makes the hot water side of the central heating more efficient and heats the hot water faster, you probably have what is known as a gravity hot water system rather than a pumped system. and possibly have an old (I'm guessing) baxi bermuda 552 fire and back boiler or something similar. if I am right don't panic I'm sure we have never met.
that should be enough info.

Answer 7

You don't say what sort of heating system you have. If it is back boiler or has been in the past, there is always one radiator, normally the bathroom, connected to the hot water circuit to disperse excess heat when the cylinder comes up to temperature. A solid fuel back boiler could not be turned off and so the excess heat needed to be bled of to stop the cylinder boiling. Modern gas or oil systems are thermostatically controlled and can turn off immediately the system comes up to temperature so not needing a bleed rad. It can be connected to the heating circuit if the system is gas or oil, not, if it still solid fuel

Answer 8

We have all our radiators turned off except the one in the bathroom for towel drying, so when the boiler comes to heat the water it also heats the towel dryer as well.

Answer 9

Its whats called a summer loop, it gives you heating to your bathroom in the summer, this giving the opportunity to dry towels & keep them warm, being an area ware you may need heat, but not require the heating to be on in other parts of the house, it can be controlled by a TRV (thermostatic radiator valve) if required.

Answer 10

That's messed up. You should fix the piping system to correct that, or install a valve on that radiator to prevent the hot water from reaching it.