2 rads not heating

abnormalnorman

hi

in the main bedroom upstairs, there is 4 rads in total. 2 large ones in line under the windows, and one small one in both the ensuite and walk-in wardrobe.

The small rads work perfect.

But the big rads dont heat up half as much. iv tried letting the air out by the top nozzle / key, and it hisses for a while (air coming out) but this hissing stops completely after 5 or 10 mins, but no water comes). i close it and it may have improved a little but still not great.

im not a plumber so may be something simple!

chuck eastwood

abnormalnorman wrote: »

hi

in the main bedroom upstairs, there is 4 rads in total. 2 large ones in line under the windows, and one small one in both the ensuite and walk-in wardrobe.

The small rads work perfect.

But the big rads dont heat up half as much. iv tried letting the air out by the top nozzle / key, and it hisses for a while (air coming out) but this hissing stops completely after 5 or 10 mins, but no water comes). i close it and it may have improved a little but still not great.

im not a plumber so may be something simple!

5 or 10 mins ? That's a whole lot of air in the system. How often do you have to do that. Have you tried balancing the system. Often the problem as water will take the easiest flow path and that might well be the two smaller rads. Have a look at a few vids on YouTube. It's worth a shot before you call in a plumber. Oh, how dirty does the water look coming out of the bleed ?

abnormalnorman

chuck eastwood wrote: »

5 or 10 mins ? That's a whole lot of air in the system. How often do you have to do that. Have you tried balancing the system. Often the problem as water will take the easiest flow path and that might well be the two smaller rads. Have a look at a few vids on YouTube. It's worth a shot before you call in a plumber. Oh, how dirty does the water look coming out of the bleed ?

thanks chuck. yes about 5 mins at least of small hissing before hissing stops but no water ever comes out of the rads.

the water in other rads would be grey.

chuck eastwood

abnormalnorman wrote: »

thanks chuck. yes about 5 mins at least of small hissing before hissing stops but no water ever comes out of the rads.

the water in other rads would be grey.

Light enough colour then it's probably (hopefully) not full of sludge. Make sure they are fully bled. Open all valves on the rads turn on the heating. Take note of the rads that get hot first. Those same rads, close off the return pipe a turn or two and give it five mins to see if the colder rads are now heating. Essentially you want to create a balanced flow through each rad by restricting those with the best flow which are often closest to the pump/boiler. Keep turning the hotter rads down until the cold rads are heating up. If this seems to be working then leave the heating off for and hour and start the heating from cold and see if the rads heat at the same page. It can be tricky but always worth trying before calling in a pro

chuck eastwood

Also these are well worth fitting if you have to bled your rads regularly

HV30 Aladdin Self Bleeding Automatic Radiator Valve 1/2" BSP Single Valve https://www.amazon.co.uk/dp/B019395RHY/ref=cm_sw_r_cp_apa_i_XVqICbH87XX1Y

jack_t

abnormalnorman wrote: »

thanks chuck. yes about 5 mins at least of small hissing before hissing stops but no water ever comes out of the rads.

the water in other rads would be grey.

Have you checked the pressure gauge to see if there is correct pressure?

Skatedude

turn off 3 rads at a time and bleed the remaining one and then swap until all rads have been bled , then get a plumber in to properly balance them and to probably top up the system
.

abnormalnorman

jack_t wrote: »

Have you checked the pressure gauge to see if there is correct pressure?

what pressure should it be at?

John.G

abnormalnorman wrote: »

what pressure should it be at?

Assuming a un vented system, 1 bar when cold and 1.5/2.0 bar when hot. Re the air releasing from two rads and no water issuing, are you sure that there isn,t a vacuum in the rads and maybe you are actually drawing air into them?. Vent them with the boiler AND circ pump off and then see if water comes out.
If it doesn,t then it might point to a defective pressure gauge as you need a minimum of 0.5/0.6 bar to overcome the static head.

abnormalnorman

John.G wrote: »

......Re the air releasing from two rads and no water issuing, are you sure that there isn,t a vacuum in the rads and maybe you are actually drawing air into them?.

you might be 100% right here John G. it might actually be a vacuum. hard to tell but it looks that way. what does this mean?

John.G

abnormalnorman wrote: »

you might be 100% right here John G. it might actually be a vacuum. hard to tell but it looks that way. what does this mean?

Still not sure if its a vented or un vented system. IF its a vented system you will or should have a small Feed&expansion tank in the attic, see if this has water in it, if not push down the ball cock as it may be stuck, you should then get water from the rad(s) air vents when the tank is ~ 1/3rd full.

IF a un vented system it will have a pressure gauge somewhere, if a gas fired boiler, it may be in the boiler panel, if oil it should be somewhere near a red expansion vessel with a filling loop (from the mains), if you have located this, get some one to watch for water issuing at the rad vents (boiler and circ pump off) while opening fill loop valves, but do not pressurize it to more than 1.5 bar, if the pressure gauge does not move, then stop as soon as water comes out of the vents.
If everything was/is normal then as stated previously, the pressure should vary between 1.0 bar& 1.5to2.0 with system cold/hot.

abnormalnorman

John.G wrote: »

Still not sure if its a vented or un vented system. IF its a vented system you will or should have a small Feed&expansion tank in the attic, see if this has water in it, if not push down the ball cock as it may be stuck, you should then get water from the rad(s) air vents when the tank is ~ 1/3rd full.

IF a un vented system it will have a pressure gauge somewhere, if a gas fired boiler, it may be in the boiler panel, if oil it should be somewhere near a red expansion vessel with a filling loop (from the mains), if you have located this, get some one to watch for water issuing at the rad vents (boiler and circ pump off) while opening fill loop valves, but do not pressurize it to more than 1.5 bar, if the pressure gauge does not move, then stop as soon as water comes out of the vents.
If everything was/is normal then as stated previously, the pressure should vary between 1.0 bar& 1.5to2.0 with system cold/hot.

ok thanks. ill check if it's vented or not.

what i find strange is that every other rad in the upstairs zone is piping hot. just these 2 double rads stone cold. the very bottom of them are hot but the rest of them cold. if it was a pressure problem then surely it would effect all the rads ???

abnormalnorman

abnormalnorman wrote: »

ok thanks. ill check if it's vented or not.

what i find strange is that every other rad in the upstairs zone is piping hot. just these 2 double rads stone cold. the very bottom of them are hot but the rest of them cold. if it was a pressure problem then surely it would effect all the rads ???

see attached pic of the pressure guage i think your on about. this is it with the system off.

as per my previous post, if twas a low pressure problem, would it not effect all the other rads? all other rads are piping hot!

abnormalnorman

abnormalnorman wrote: »

ok thanks. ill check if it's vented or not.

what i find strange is that every other rad in the upstairs zone is piping hot. just these 2 double rads stone cold. the very bottom of them are hot but the rest of them cold. if it was a pressure problem then surely it would effect all the rads ???

see attached pic of the pressure guage i think your on about. this is it with the system off.

as per my previous post, if twas a low pressure problem, would it not effect all the other rads? all other rads are piping hot!

John.G

Picture not attached yet. john

abnormalnorman

abnormalnorman wrote: »

ok thanks. ill check if it's vented or not.

what i find strange is that every other rad in the upstairs zone is piping hot. just these 2 double rads stone cold. the very bottom of them are hot but the rest of them cold. if it was a pressure problem then surely it would effect all the rads ???

see attached pic of the pressure guage i think your on about. this is it with the system off.

as per my previous post, if twas a low pressure problem, would it not effect all the other rads? all other rads are piping hot!

John.G

Yes, if that pressure gauge is reading correctly then that should be fine and water should come out of the air vents on all the rads at the same level, you said that once the air stops then no water comes out and that's why i suspected air ingress to those two rads.
AS suggested above have you ran the system with just those two rads on to see if you can force any air locks (if present) from the system. Have these two rads ever heated up properly?

Can you increase the pressure by opening that black knob, you may find that it is already left open (auto fill) to maintain just > 1.0 bar (cold) and what is the pressure showing when the system is hot?.

abnormalnorman

John.G wrote: »

Yes, if that pressure gauge is reading correctly then that should be fine and water should come out of the air vents on all the rads at the same level, you said that once the air stops then no water comes out and that's why i suspected air ingress to those two rads.
AS suggested above have you ran the system with just those two rads on to see if you can force any air locks (if present) from the system. Have these two rads ever heated up properly?

Can you increase the pressure by opening that black knob, you may find that it is already left open (auto fill) to maintain just > 1.0 bar (cold) and what is the pressure showing when the system is hot?.

thanks John G

i ran the system with only one rad on, all others off, and it made things worse! both rads barely getting warm now. a lot of gurgling , and air (either sucking or blowing) out the vents, but this air eventually stops but no water.


before when these rads got cold, i used be able to open that black knob and leave for a while and the pressure used go right up , and the rads used then work fine. but this would only last a month before needing to do it again. but now it appears this black knob is doing nothing when i turn it. and pressure seems the same when system on or off!. maybe thats my problem. This guage cud be stuck. but must be leaking pressure somewhere then?!

John.G

More than likely that the gauge is stuck. IF you can isolate/drain the system then renew that pressure gauge and take it from there. Eventually I think you will have to drain the system (renew the pressure gauge) and check that the pre pressure in the e.vessel to 1.0 bar and then cold fill it to 1.5 bar and see how you go from there.

abnormalnorman

John.G wrote: »

More than likely that the gauge is stuck. IF you can isolate/drain the system then renew that pressure gauge and take it from there. Eventually I think you will have to drain the system (renew the pressure gauge) and check that the pre pressure in the e.vessel to 1.0 bar and then cold fill it to 1.5 bar and see how you go from there.

thanks John G. only thing im wondering is how all other rads are working perfectly??

Wearb

It could be that turning that black knob has no effect because that auto fill valve is set to too low pressure. I.E. if its set to 1.25 bar, then turning the knob will never give you more than 1.25 pressure. 1.25 should be enough if the gauge is working correctly.

abnormalnorman

But how come some of the rads are working ok??

if it is a problem with pressure, wud it not effect all rads?? . Anyway, ill probably replace that whole unit then, guage and black knob n all.

to do so, i take it i just isolate it (shut valves off) at both ends( if i can find them), replace, then turn valves on again?

agusta

abnormalnorman wrote: »

great . thanks all. ill probably replace that whole unit then, guage and black knob n all.

to do so, i take it i just isolate it (shut valves off) at both ends, replace, then turn valves on again?

i doubt you have shut off valve at both ends...

abnormalnorman

just an update . .. .

in my desperation for heat at 5am this morn, i went out and opened up that black knob. i gave the guage a tap of the hammer, and lo and behold, it went to zero. I then gave the whole black knob unit a few flakes of the hammer, and lo and behold again, the pressure started to rise.

All rads working full throttle now!

pressure was at 2.5 bar with system off this morn !!!! And water leaking out the red pressure release before entering boiler. , so iv turned black knob off. prob shud now replace this piece.

thanks all for the help.

John.G

abnormalnorman wrote: »

just an update . .. .

in my desperation for heat at 5am this morn, i went out and opened up that black knob. i gave the guage a tap of the hammer, and lo and behold, it went to zero. I then gave the whole black knob unit a few flakes of the hammer, and lo and behold again, the pressure started to rise.

All rads working full throttle now!

pressure was at 2.5 bar with system off this morn !!!! And water leaking out the red pressure release before entering boiler. , so iv turned black knob off. prob shud now replace this piece.

thanks all for the help.

Glad you are (almost) sorted. In the meantime keep that black knob closed until eventually the pressure (WHEN COLD) falls to ~ 0.7 bar (might have to use "hammer" on gauge) then crack open the black knob to give 1.0 to 1.25 bar and then re close it. This should result in a HOT system pressure of ~ 2 bar, if it reaches ~ 3 bar the PRV (pressure relief valve ) on the boiler will lift.