Boiler making noises after drain and refill of system

[dmjones500]

Hi everyone,

I recently drained and refilled my sealed, combi-boiler system. I bled the radiators but did nothing to the boiler. It has an automatic air vent, which I think is open (it is a little raised, seems to possibly bubble a bit).

This morning, the boiler started making some unpleasant noises (my wife described it as like an aeroplane flying overhead). The noises came and went at regular intervals and appeared to be getting louder each time. Each time the noise occurred, it was preceded by a hissing noise which increased in intensity, followed by a loud hum which peaked and disappeared.

So... I'm debating whether I have some air in my boiler pump. Or perhaps I just have crud in my system, perhaps loosened by my recent draining. I plan to flush the system this evening, followed by adding Sentinel X400 and running for a few days. Then I plan to flush down and add some Sentinel X100 inhibitor before leaving it for good.

So, my question is basically this: do my current symptoms sound like air in the boiler? Or something else? If it sounds like air, should I perhaps manually bleed the pump (i.e. turning the big screw)?

Would it be just as wise to ignore the current noises, flush the system and proceed with my de-gunging efforts?

Note: I've not been running the boiler all day, just in case the noises were the sound of my boiler ripping itself apart!

Thanks in advance,
Duncan

 

[dmjones500]

FYI - I'm currently draining again, with the aim of refilling with some X400 in the system.

I'm grateful for any advice on the original question, however, as I'll be refilling tonight and want to pre-empt any problems.

I had an experimental tweak on the large screw on the pump, but it didn't want to budge and I didn't want to force it!

 

[plumbnuts]

Persist with the screw in the centre of the pump - it opens anti clockwise. Do this with the boiler off and until you get a small trickle of water out. When filling the system, vent the downstairs rads first.

Steve

 

[dmjones500]

Persist with the screw in the centre of the pump - it opens anti clockwise. Do this with the boiler off and until you get a small trickle of water out. When filling the system, vent the downstairs rads first.

Steve

Thanks for the tip, I'll give it a go this evening and will post back with results.

That is, after I replace this leaky drain valve which is making emptying my system a royal mess.

 

[dmjones500]

By the way, should I bleed the pump before or after bleeding the radiators?

 

[plumbnuts]

After would ensure that there is no air in the pump.

 

[dmjones500]

After would ensure that there is no air in the pump.

Hi again,

I've finished draining and filling (and replacing leaking drain valve ).

I vented downstairs radiators, then upstairs. System is pressurised to 1.25 bar now.

I tried to vent the pump, by unscrewing the large screw. A smidgeon of water came out. I then stumbled across http://www.pumptool.co.uk/Combi Boilers.html#venting, which gave a great explanation of how to vent. I tried to follow this, turning the pump several times anticlockwise in an effort to free any air. Unfortunately, I couldn't tell if this was doing anything or not.

Anyway, I finally fired up the pump and heard a great deal of air (I think) in the system. The burner duly cut out after 20-30s or so, which means I guess the air is still an issue.

Any more ideas for venting my boiler? Do I just need to stick with it longer?

Thanks in advance,

Duncan

 

[JohnD]

sometimes the air will find its own way out over time, or if you repeatedly turn the pump on and off for short periods (you may hear it bubbling round when you do this). Turn the boiler stat down as far as it will go (or off) so that it does not overheat if there is poor circulation.

Keep bleeding the rads and pump as the air moves around. You may need to repressurise it if you bleed it a lot.

I am a householder not a pro.

 

[dmjones500]

sometimes the air will find its own way out over time, or if you repeatedly turn the pump on and off for short periods (you may hear it bubbling round when you do this). Turn the boiler stat down as far as it will go (or off) so that it does not overheat if there is poor circulation.

Keep bleeding the rads and pump as the air moves around. You may need to repressurise it if you bleed it a lot.

I am a householder not a pro.

Thanks, I'll bear this in mind over the next few days.

I just solved the problem, by realising I had tightened up the automatic air vent. I loosened this and restarted the boiler. Almost immediately it was better and now is running ok.

I had to close it back down again, however, as it started to really spew water. Is this normal? Or is in indicative of an automatic air vent that needs cleaning/replacing?

Thanks in advance,

Duncan
(getting there slowly)

 

[JohnD]

can't help you with the AAV I'm afraid, as I have no experience there, though I've heard they can jam (or fill up with sediment).

Post a pic and I expect someone will know what to do.

 

[dmjones500]

can't help you with the AAV I'm afraid, as I have no experience there, though I've heard they can jam (or fill up with sediment).

Post a pic and I expect someone will know what to do.

I've definitely concluded the AAV is screwed. It spews water whenever open. I'll have to replace it.

The manual refers to "draining the primary circuit". I have a horrible feeling this means "undo the work of the evening and drain the whole CH system". Is that right?

I would run the system with the AAV closed, but I've heard this is a bad idea, plus my boiler is not completely running noise free, so I suspect some air is making the rounds regularly.

 

[JohnD]

just keep bleeding the rads and pump. If your circulation is generally good and the pump is not hot, small bubbles will tend to get squirted round until they collect in a radiator. You can loosen the AAV to check.

I take it you have a pressurised sytem, with no Feed & Expansion tank in the loft? If you undo just the drain-off cock, some water will squirt out until the pressure is lost. Then it will stop. Close the DOC and when you open the AAV, no water, or very little, will leak out. If you have the new part to hand, you can probably get by without draining down, just using a few old towels to collect drips and dribbles. One of the beauties of working on a sealed sytem is that if air can't get in, the water won't come out (much)

The filling loop must of course be turned off and disconnected.

 

[dmjones500]

One of the beauties of working on a sealed sytem is that if air can't get in, the water won't come out (much).

Ah, cunning plan. I'll give that a go, thank you.

 

[twgas]

If you've added the X400 already wait until you drain/flush it out, the cleanser will loosen/release debris from rads which may just ruin the new aav, check for air by opening the aav daily - the amount should reduce every day.