All radiators working bar one? System boiler?

Mayo Exile

Hi all. All my radiators are working bar one. I turned all the others off then it worked. Then I turned the others back on and the one that wasn't originally working went cold again???:(

System is heated by natural gas. Bathroom has just been tiled and the radiator there was taken off. The tilers got a plumber to re-attach the radiator. This radiator, I noticed, was only warm at the bottom. I bled it. Then air, some dirty water, and finally clean water came out. radiator worked ok after this. Bled the cold radiator, (water came out, no air) but radiator stayed cold. Checked all radiators, no air in any. All still hot. Heating system was on at the time. Would bleeding radiators affect pressure in system hence the one cold radiator, or is it an airlock maybe?

Thinking, it might be a pressure problem, checked the pressure gauge at the combi cylinder (pictures 1 and 2). it was reading zero. Turned black knob anti-clockwise. Went to just over 1 bar. Left knob in that position. Also checked gauge on the natural gas boiler (Picture 4). Not sure if its a system or a combi boiler. Boiler is a Mini "Ideal". Would it be a system boiler when i have the combination cylinder as well? It's reading 0 bar with boiler off. (same too when on). Is this right if it's a system boiler?

By bleeding the radiators have I reduced the pressure? However all the remaining radiators still are OK (bar one) with boiler operating despite pressure being 0 bar. I thought the boiler wouldn't operate when this happens? Read in other threads about a "filling loop" to repressurise the system. However I can't see one near the boiler (picture 5 - view of bottom of boiler). That if its there at all.

Separately, I also noticed the stopcock on the "hot water in" pipe to the combi cylinder was nearly closed (picture 6). I opened it fully. Is this correct?

Pete67

Around 1 bar is fine, check it again when the heating system has been off for a while and everything is cold. Adjust the pressure regulating valve to 1 to 1.5 bar and then close the red hand wheel valve below it. This prevents the heating system topping up constantly which can hide the presence of a leak. Check the pressure ocasionally and top up as needed. You should not need to add water very often. If the need to top up increases suddenly you know you have a leak and can investigate and repair.

When you bleed air out of radiators, you drop the system pressure, so before starting make sure the pressure is above 1 bar and then keep an eye on it as you go around. If you allow the pressure to drop when bleeding you can actually draw air into the radiators, especuially on upstairs ones. It is better to bleed the system when it is cold, as hot water contains more dissolved gases than cold, so it is easier to remove them cold. Also bleed radiators with the pump switched off as it can create localised low pressure areas and may cause air to be pulled in rather than out.

The cold radiator is due to poor system balancing, especially if it works when the other are off. Each radiator has two valves, one with a handwheel or thermostatic head, and the other with a plain plastic cap, called the lockshield valve. If you want to balance it yourself you need time and patience. Go around all the radiators, fully open the handwheel valves or remove thermostatic heads if fitted, remove the caps from the lockshield valves, close all lockshields fully and then open each on say 1/2 a turn. Fire up the boiler at maximum temperature, and go round all the radiators. Find the ones that heat up fastest, and close the lockshields a little. You may also need to open the lockshields on any that do not heat properly. If you really want to do it properly, adjust each lockshield so the the return water temp from that radiator is 10 degC colder then the supply water temp. You will need a couple of digital thermometers to do this, handheld contact probes will do fine. If it's a condensing boiler aim for 15 deg temperature drop at each radiator as this allows the boiler to run more efficiently.

The valve you mentioned in pic 6 looks more like its in the hot water supply to the shower pump in the bottom of the hot press. If so it should be fully open.

Mayo Exile

originally posted by Pete67: Around 1 bar is fine, check it again when the heating system has been off for a while and everything is cold. Adjust the pressure regulating valve to 1 to 1.5 bar and then close the red hand wheel valve below it. This prevents the heating system topping up constantly which can hide the presence of a leak. Check the pressure ocasionally and top up as needed. You should not need to add water very often. If the need to top up increases suddenly you know you have a leak and can investigate and repair.

Thanks Pete67. This is the dial beside the combi water cylinder? (see picture). I had turned the black knob all the way anti-clockwise. Left it in this position. Its reading 1 bar. Same as last night. Have closed red valve below it. Still reads 1 bar.

What about the pressure reading on the gas boiler itself? Should this be at 0 bar? Or does it matter for a system natural gas boiler?

Might have a go at fixing the cold radiator if I build up enough patience!

Should also add that that ALL the radiators were fine before the radiator in the bathroom was removed and re-installed. Then the one described in post #1 went cold.

Property is a ground floor apt.

JamesM

Check the speed of the water circulating pump. It should have a switch with 2 or 3 speeds. If it is at a lower speed turn it up.
Jim.

Pete67

OK, valve with red handle is an isolating valve. Leave this closed except when you are adding water to re-pressurise the system. Above that (not captioned in your pic) is a non-return valve (to prevent backflow from the heating system to the mains water supply). Above that again is a pressure regulating valve, which limits the pressure you can apply to the heating system. The pressure regulator is adjustable by the brass screw on the left hand side in the pic. You should not need to adjust it as it seems to be working OK. The black knob on the regulating valve is just another isolating valve to prevent the system from filling without your knowledge.

So, to top up the pressure, open the red valve, then open the black knob on the regulator, pressure should rise to around 1 bar, close black knob and then red valve. Check pressure once a week or so to make sure it is not dropping excessively.

When you are venting the radiators, you can leave both the red valve and the black knob open to prevent the pressure dropping when the air is being forced out.

Chances are the setting of the lockshield valve was changed on the radiator that is now cold when it was removed, as both valves would have been closed tight. You can open it 1/4 turn at a time until is is working fine again.

Mayo Exile

Originally posted by Pete67:Chances are the setting of the lockshield valve was changed on the radiator that is now cold when it was removed, as both valves would have been closed tight. You can open it 1/4 turn at a time until is is working fine again.

Thanks Pete67. The radiator in the bathroom that was removed and put back on is ok. It was only heating at the bottom at first. Some air, then dirty water and finally clean water came out. It was a radiator in a room next to the bathroom that went cold. This radiator was working ok before this.

The pressure is now reading 1.5 bar.

What about the pressure reading on the system boiler itself? Still reading 0 bar with the boiler operating.

Apologies for any confusion.

Pete67

Mayo Exile wrote: »

Thanks Pete67. The radiator in the bathroom that was removed and put back on is ok. It was only heating at the bottom at first. Some air, then dirty water and finally clean water came out. It was a radiator in a room next to the bathroom that went cold. This radiator was working ok before this.

OK, probably an airlock in the pipes somewhere. Close off all the other radiators and try to force the air up into the radiator that is not working by running the boiler. Then vent the radiator again.

Mayo Exile wrote: »

The pressure is now reading 1.5 bar.

What about the pressure reading on the system boiler itself? Still reading 0 bar with the boiler operating.

Apologies for any confusion.

The two gauges should read more or less the same pressure when the system is switched off. If not, one of them is not working properly. It is common for the gauge at the boiler to be connected to the suction side of the pump, so will read a lower pressure when the boiler is running.

Mayo Exile

Originally posted by Pete67OK, probably an airlock in the pipes somewhere. Close off all the other radiators and try to force the air up into the radiator that is not working by running the boiler. Then vent the radiator again.

Tried this. All radiators seem fine now! Pressure at gauge by the cylinder just slightly over 1 bar (system on). Pressure on gas boiler gauge remains at roughly 0.2 bar. Thanks!

Pete67

Mayo Exile wrote: »

Tried this. All radiators seem fine now! Pressure at gauge by the cylinder just slightly over 1 bar (system on). Pressure on gas boiler gauge remains at roughly 0.2 bar. Thanks!

You're welcome! Out of curiousity, what is the reading on the two pressure gauges when the boiler/pump is switched off?

By the way, it is normal for the pressure to increase when the system heats up, and drop again as it cools down. This is due to the thermal expansion of the water as it gets heated. It should be around 1 bar cold, as long as it does not increase towards 3 bar when hot then its fine.

Mayo Exile

about 0.5 bar on the gauge by the cylinder and about 0.2 bar on the gas boiler gauge.

Pete67

Those pressures are a little low, but if it's working OK they are fine. The difference between the two gauges is not that significant. If you want to pressurise the system up to 1 bar when it's stone cold with no boiler running you can see if both gauges increase. Then when the system is hot, the pressure should increase further by a little. It should not go above 2.5 bar and ideally should be less than 2.

Mayo Exile

Those pressures are a little low, but if it's working OK they are fine. The difference between the two gauges is not that significant. If you want to pressurise the system up to 1 bar when it's stone cold with no boiler running you can see if both gauges increase. Then when the system is hot, the pressure should increase further by a little. It should not go above 2.5 bar and ideally should be less than 2.

Ok. Thanks. Gauge by the cylinder is about 1.2 bar with system running while gas boiler gauge is still roughly at 0.2 bar.

I'll switch it off later and check the pressures when system is cold in the morning. Post again then.