High pitched whine that rises and falls for hours after central heating has been on

[morty1]

Same thought :


Tried turning one rad off at a time, overnight, in case it's one of the rads?

yeah, i shut off the large radiator across from the small one that seems to be where the noise is focusing. I'm just surprised at how much air is still moving through the system considering its only 4 rads and there's 2 auto air vents. one on the boiler and the other after the last radiator.

 

[Daveydub]

It may be that when heating is running aavs are at negative pressure so allowing air to be drawn in.
With heating off and after the noise has stopped, tighten the dust caps on the aavs.
If this cures it then replace aavs with manual vents

 

[Johntheo5]

Hi All,
Recently had a loft conversion done. 2 bedrooms and a bathroom. One large radiator in one room, bathroom has a towel radiator & the other room has one large radiator & a small one on the opposite wall. I obviously expected it would take a bit of time to get rid of the air after a bleeding the radiators over a couple of weeks & a few glugs and rattles from the radiators when in use is to be expected. There's also an auto air vent fitted at the end of the pipework after the last radiator.
The problem is that an hour or so after the heating goes off i get a high pitched whine that rises and falls and seems to resonate to the small radiator. I've adjusted the lockshields a little bit not that the radiators need balancing they are all so hot you could cook steak on them within minutes & I mean ferociously hot above setting number 2.
The whine goes on all night hour after hour its that bad you cant sleep in the room. The sound rises and falls about 6-8 times a minute so at night you can imagine 8 hours of it. jeez
I think its trapped air but i thought I'd ask around to see if there's any way of resolving it as the plumber seems to not have a clue.
I've left the heating on for 3-4 hrs to see if that purges it. ( the rooms are desert hot in 20 mins)
Your help is appreciated.
Oil fired central heating system. heating system is vented. standard s plan down stairs and added an extra 2 port valve to operate heating upstairs.

Get someone to start and stop the boiler while you watch the vent (over the feed and expansion cistern for any spurt of water both while its starting and also just after it stops., also see if any pump over through the vent while the boiler is on. What make/model/mode/setting is the circ pump, if it has LEDs, post a photo while its running. Any idea of the vent and cold feed arrangement?.

 

[morty1]

Same thought :


Tried turning one rad off at a time, overnight, in case it's one of the rads?

tried it, made no difference unfortunately

 

[morty1]

It may be that when heating is running aavs are at negative pressure so allowing air to be drawn in.
With heating off and after the noise has stopped, tighten the dust caps on the aavs.
If this cures it then replace aavs with manual vents

I'll give that a go. one is fitted right next to the burner and the other is in the room where the noise is occurring but on the opposite side of the room. The green circle area is where the sound appears to be resonating

 

[morty1]

Get someone to start and stop the boiler while you watch the vent (over the feed and expansion cistern for any spurt of water both while its starting and also just after it stops., also see if any pump over through the vent while the boiler is on. What make/model/mode/setting is the circ pump, if it has LEDs, post a photo while its running. Any idea of the vent and cold feed arrangement?.

I'll have a look and get back to you.

 

[morty1]

Get someone to start and stop the boiler while you watch the vent (over the feed and expansion cistern for any spurt of water both while its starting and also just after it stops., also see if any pump over through the vent while the boiler is on. What make/model/mode/setting is the circ pump, if it has LEDs, post a photo while its running. Any idea of the vent and cold feed arrangement?.

Hi, The boiler has always been in the garage and now the header tank is also in the garage so the pipe run from the boiler to tank is less. Basically the two boiler to tank connections were just rerouted from where they went through the wall to the loft to the top of the garage to where the tank is. The cold feed to the expansion tank was taken from a feed that was already in the garage which comes from the mains supply. Tank is full and operating as it should. pump is set on speed 1

 

[dilalio]

If it goes on for hours after Heating gone off, it sounds unlikely to be anything mechanical... CH wise that is.

I'd close those AAVs.

 

[morty1]

If it goes on for hours after Heating gone off, it sounds unlikely to be anything mechanical... CH wise that is.

I'd close those AAVs.

You got me thinking after you mentioned the AAV's Looking at the one at the boiler am i right that the AAV should be on the pressure side of the pump?? if that's the case its on the wrong side. I assume to close them its just a case of screwing the plastic cap in??? it appears that one is closed so whether he just fitted it to bleed the system I've no idea. kind off defeats the purpose of having it??

 

[Johntheo5]

Hi, The boiler has always been in the garage and now the header tank is also in the garage so the pipe run from the boiler to tank is less. Basically the two boiler to tank connections were just rerouted from where they went through the wall to the loft to the top of the garage to where the tank is. The cold feed to the expansion tank was taken from a feed that was already in the garage which comes from the mains supply. Tank is full and operating as it should. pump is set on speed 1

The cold feed (and vent)I'm referring to to is where the (cold) feed is teed into the system, a fairly commonn arrangement is where, from the boiler you have the vent then the cold feed (no more than 150mm apart) and then the pump, see if yours is like this, I would still look into the feed & expansion cistern as suggested, if shutting off that wrongly positioned AAV doesn't cure the problem, then, and depending on what you see happening in the cistern, you might change the pump mode/setting to (proportional pressure) PP III (the highest PP setting) even though it migh be a bit on the weak side but its only the press of a button.

 

[morty1]

The cold feed (and vent)I'm referring to to is where the (cold) feed is teed into the system, a fairly commonn arrangement is where, from the boiler you have the vent then the cold feed (no more than 150mm apart) and then the pump, see if yours is like this, I would still look into the feed & expansion cistern as suggested, if shutting off that wrongly positioned AAV doesn't cure the problem, then, and depending on what you see happening in the cistern, you might change the pump mode/setting to (proportional pressure) PP III (the highest PP setting) even though it migh be a bit on the weak side but its only the press of a button.

If I'm understanding you right. On the left side of the boiler the cold feeds at the bottom & the vent is the top pipe. The reason the pumps always been on setting 1 is that even before the extension when the pumps put on 2 or 3 the TRV's bounce and i presume the only remedy would be to fit bi directional ones???. I'll definitely check the feed & expansion.

 

[Johntheo5]

The pipes above are the boiler flow (top) and return (bottom), the vent will be teed off this somewhere like below and the cold feed is teed in generally just after it but may be teed into the return on some systems. The system below is called a close coupled system.

 

[morty1]

The pipes above are the boiler flow (top) and return (bottom), the vent will be teed off this somewhere like below and the cold feed is teed in generally just after it but may be teed into the return on some systems. The system below is called a close coupled system.

View attachment 399206

the 2 pipes i showed, the bottom is straight from the expansion tank cold supply the top is the vent that goes to the expansion tank. on the right hand side there's the flow at the top and the return at the bottom????

 

[Johntheo5]

Very good, thanks, so all 4 connections are used on the boiler, should be OK then as long as no blockage or partially blockage where the cold enters the boiler.

 

[morty1]

Very good, thanks, so all 4 connections are used on the boiler, should be OK then as long as no blockage or partially blockage where the cold enters the boiler.

yeah they flushed it as it was pretty dirty before they refilled. i mean its all pretty much straight runs with 2 off the radiators teed off. just cant understand where the noise is coming from. The boiler is "old" but there's zero problems with the heating downstairs.