UKC

so we have one radiator in the house that I just cannot seem to switch off, which isn't ideal in hot weather. valve on the radiator itself is turned right down, appreciate this valve may be faulty, but also the main thermostat for the house is turned right down and central heating system itself set to off. New-ish combi boiler, i think the whole system needs a good flush through, but until i can afford that would like to turn this one radiator off!! any ideas??

In reply to d508934:

Is it coming on when you're heating water? (ie when the boiler is firing?) Ours does that. There's a switch box thingy in the cylinder cupboard which controls this and needs replacing but I haven't got round to it yet.

In reply to Alyson:

no, comes on and off throughout the day and night!

In reply to d508934:

Have you tried taking the thermostat off the rad and inserting a 5p coin and replacing.
sometimes the thermo doesnt depress the valve pin enough

In reply to WildCamper:

haven't tried but sounds like worth trying. was just assuming that master controls for the house would do the trick!

In reply to d508934:


Presumably your hot water does too.

The valve Alyson means is the Y valve. If you've got a combi you won't have a cylinder so it's not likely to be some hot water getting to the nearest radiator.

In reply to Philip:

why would hot water come on throughout the night? don't combi boilers fire up when tap is switched on?

In reply to d508934:

Our combi boiler has a button which toggles between Eco & Quick. If on quick, you will get hot water quickly, if on Eco it will take a couple of minutes to come through. The downside is that the Quick setting means that it fires up periodically. So we set it to Eco.

Also, we have one radiator in the system which is first in the circuit and cannot be turned off or down if the boiler is on. Not sure why.

In reply to lowersharpnose:

Older systems had a radiator that stopped the boiler short cycling when just heating water.

The boiler would be too big to just heat hot water so would end up switching on and off too much and too often - short cycling.

In reply to lowersharpnose:


https://www.google.co.uk/search?q=bypass+radiator

If you turned all of the radiators down then how would the pump continue to keep the water moving?
If the water stops moving you may damage the pump or have a boil off in the heat source.

In reply to d508934:

Have you noticed if it only gets warm when hot water is run, because a faulty diverter valve would cause this.have you tried switching the boiler to hot water only?

In reply to interdit:

The water can still circulate,heating runs in a circuit and the feeds for the radiators are tee'd from this unless you have a very old and very poor one pipe system which runs through in each radiator but that's unlikely on a modern combi

In reply to Wsdconst:

Heating runs in a circuit, as you say, but it's not uncommon to see no direct return and a bypass radiator is often in place instead. This will have no trv.

In reply to d508934:

Do you have cold spots on other radiators when the heating is on? This would indicate you need a flush.

Your radiator may be the boiler bypass, in which case it needs to be left alone. Is it only getting hot when hot water is being used?

In reply to interdit:

Yeah I've seen this on towel rails before.

In reply to marsbar:

certainly does need a flush, cold areas at the bottom of most rads when system switched on. rad comes on and off throughout the night so not related to hot water coming on. will investigate the boiler to see if it has a hot water only option. it's a newish boiler but an old house so suspect the piping may be donkeys years old; if so maybe this is a bypass rad, new to me but will investigate!

thanks for the tips everyone!

In reply to d508934:

It's the boiler switching on and off randomly at night that's most puzzling if all the controls are shut down. Might be time to dig out the manuals, see if it's maybe been left in some sort of frost protection mode. Is there a timeclock built into the boiler as a basic control in addition to the thermostat/programmer in your hall/lounge?

jk

In reply to jkarran:

yes this is what has puzzled me most, how it could come on and off repeatedly when everything is switched off. good idea with the manuals, frost protection sounds possible (although affecting only one rad seems odd still) - but will have a look through the manual

In reply to lowersharpnose:

This radiator is a heat sink (dump). If you have a boiler producing hot water (or running the whole system) and the hot water is suddenly turned off, it takes a short time for the gas to shut down and the very hot water (or steam!) produced during this short time has to be dumped, and the permanently on radiator is there for that reason. If you want a scary experiment, run the hot tap, and turn it and the power to the boiler off at the same time. The system will bang and rattle until the water in it naturally cools. Most modern combies specify a heat sink (dump) radiator for safe operating.
The eco setting shuts everything down completely and so has to restart from completely cold (that includes some water and the metal parts of the boiler.) when you need water/heat. The quick setting keeps the small amount of water and the metal parts of the boiler warm, ready for almost instant supply.

In reply to d508934:

That one rad is almost certainly the lowest resistance path on the circuit, either because it's set up as a bypass, or a valve is stuck. All the rest of your rads with TRV's will be shut down hard this time of year.

Another possibility is that pressure fluctuations in your water supply or a leak on the hot water system are triggering the boiler into heating hot water when it's not demanded, the boiler will quickly get too hot and shut down but the heat then has to go somewhere and that somewhere may just be the nearest rad. It's unlikely but if all else fails it's a possibility. I know when I was de-pressurising and re-pressurising my water system recently (combi boiler) for some work on the bathroom I observed some odd behavior from the boiler, it was running its blower and starting the ignition sequence when I opened the kitchen cold tap. I thought for a moment I'd cocked something up it was just fluctuating pressure caused by air in the system and a partially closed stop-tap.

jk

In reply to d508934:


My understanding from what my heating engineer said, assuming no faults with say frost stat, thermostat, etc, is some modern boilers are so clever that they regularly automatically start up at times when not used (summer) to keep pump, seals, values, in working order. They also have a run on system to dissipate unwanted heat after shutdown.

Also as someone mentioned modern combi boilers usually have a setting for quick supply of hot water - this of course has to be kept topped up. If it's a large boiler then starting up will produce a lot of heat quickly and if this is more than needed for topping water temp up then it has to be dumped some where.

I think you need someone to examine your system to see how yours is set up. My set up does not need a dump radiator, but does it internally somehow (not that I know how, but I hear it running without the flame on).