Gurgling radiator after using tap

[vitor710]

I haven't found a cure yet. Boiler has just been serviced, and all seems OK on that side. I'm checking the entire system for leaks. Fearing that perhaps there is a problem somewhere not easily accessible...

Your mileage may vary.

I spoke to a BG engineer before and he mentioned the same as what Madrab said.

When the diverter valve switched back DHW to CH, a shock valve was sent to the heating system. If some air is inside the pipe, the sound will be amplified and causing some noise on a faulty/low quality TRV.

I tried turned off the TRV and the sound was gone, but when I put my ear on the floor, I heard a whooshing/vibrating sound in the pipe.

I have some vertical radiators and the extra air in the system seems never gathering in these radiators.

I bled tons of water out from the problematic radiators and the sound was gone even TRV was opened. I am still monitoring the system.

 

[Madrab]

No, nothing substantial in term of pressure drop

less liable to be air then, if there was a leak there would be a noticeable pressure drops @ the boiler.

I reckon you're just getting flow noise when the diverter's switching over, especially if the CH's calling, the HW is run and the diverter switches priority and then it's back to CH again. The pump's always running, so there may be a sudden rush of flow as the diverter shifts.

That then creates a bit of turbulence in the supply pipework, especially if it is a bit convoluted and that can create noise at the valve.

 

[ChrisJP]

This seems to be a downside of combi boilers that heat domestic HW solely on demand. I think this means (though I guess you could design a boiler with 2 separate heat exchangers) that there can't be total separation of the DHW and CH water circuits and, instead, a valve has to be used to direct water heated by the boiler either to the CH circuit or the DHW taps.
The now considered old fashioned systems with a HW cylinder heated via a coil connected to a circuit from the boiler, but completely separate from the DHW in the cylinder, didn't have this issue

 

[Ade75]

It will be to do with the boiler switching over and the flow starting up again in the system and it's moving past a noisy valve, especially given it's at the top of the house where any air in the system will naturally gravitate to. Do you find that rad needs bled more often?

That one radiator seems to be the only one that needs to be bled regularly. Definitely a bit of air bubbling up into that one when taps are turned on/off, even when heating is off (e.g. late evening when heating has been off for over an hour). So is it possible that some air enters when the diverter switches? It's a 17 year old boiler, so I imagine it's nearing end of life.

 

[Madrab]

So is it possible that some air enters when the diverter switches?

Not really, again if air is getting into the system then that means that water is getting out. If water is getting out then there would be a pressure drop. Air can get into the system when the pump kicks in and forces dissolved O2 out of the system water. That should eventually stop though once all the O2 is used up and that's more so with recently filled systems.

The alternative is as was suggested earlier whereby system corrosion is creating Hydrogen but the system water would usually be dark/black when that starts to occur. Unless the system is overly alkaline and there's aluminium present, say in the main Heat Exchanger but again that's quite specific.

I wouldn't be overly worried about the system as it sounds

 

[Ade75]

Thanks everyone. Given the system does need a small top up every few weeks, I imagine there is a small leak somewhere. But sounds like not enough to worry about - although I will keep checking. I'll try not to worry, but when water's involved I always tend to!

 

[ChrisJP]

Thanks everyone. Given the system does need a small top up every few weeks, I imagine there is a small leak somewhere. But sounds like not enough to worry about - although I will keep checking. I'll try not to worry, but when water's involved I always tend to!

Even if it's a small leak, it's worth trying to find it and repairing it. Even a small leak will require new water to be continually added to the CH circuit, introducing new oxygen and diluting the inhibitor. So corrosion within the system will be increased.

 

[Madrab]

Depends, if it can be found relatively easily, then ideally yes. All depends on how much water you're putting in and how often as to how much it'll actually dilute

 

[Ade75]

I'll certainly try to locate the leak, if indeed there is one. Would it also be worth adding a new dose of inhibitor to mitigate any issues with dilution?

 

[Madrab]

I'll certainly try to locate the leak, if indeed there is one. Would it also be worth adding a new dose of inhibitor to mitigate any issues with dilution?

again, it all comes down to how much water you've had to put in since it was last dosed as to how diluted the original dose is now and how much new O2 has been introduced