Bleeding radiators and jet engines

[Hugo Nebula]

My CH system (std boiler, vented HW cylinder, header tank, pump, etc., if you're asking) has developed a fault.

A couple of weeks ago, I noticed a leak from around the pump (replaced about 2-3 months ago). It hadn't been leaking since the pump was installed, but probably weeping for a few days. Nevertheless the installer came & replaced the seal. Fine, no leaks.

A few days ago, I noticed that the upstairs radiators needed bleeding. After bleeding the radiators a small amount of air came out. However, immediately afterwards, the pump became extremly noisy (hence the 'jet engine' subject), and the water was 'whooshing' through it, like in waves. Water through the radiators is also noisy. It settles down about a minute after the boiler firing, but starts every time it fires up.

It's been noisy since, and I've had to bleed the radiators again today. I've tried the pump on low, medium and high, but it doesn't make a difference.

Does anyone have an idea what's causing this, and could it prove rapidly fatal?

[Grimly Curmudgeon]

Classic sign of a decent amount of air being mixed up and swirled around the system by the pump. Switch the pump off for an hour, let the air come out into the tops of the rads and bleed again. Do this a few times over the next couple of days. Unless your system is drawing in air, it should all go.

[polygonum]

Did you check it was air coming out? Not hydrogen?

[A.Lee]

Did you bleed it with the pump on? If so, the air you thought had come out could actually be air that was being sucked in. Bleeding should be done with the pump off.

[Dave Liquorice]

Have you bled the pump?

[Jim K]

or did your "plumma" bleed the pump? is there an air leak on the new pump seal he fitted? get him back in

Jim K

Jim K

[Brian Gaff]

Hydrogen?

Boom..

Brian

[harry]

You may find air is being sucked down the vent pipe. This can be due to a bad layout or the pump is too big/set too high. Put your thumb over the vent pipe while someone else starts the pump, you may feel the suction.

[polygonum]

Well, burning it is how you tell...

[Jim K]

??? shurely you'd notice that no water came out of the bleed valve to signify the end of the supposed air venting??

also there is usally a distinctive smell to the "air" that should be coming out....

I don't.

Jim K

[Jim K]

cracking way of solving the problem... blow the house up ;>)

Jim K

[Mr Pounder]

I have not needed to bleed my rads for years. I did it with the system off. How many times do you bleed your rads?

[Roger Mills]

When the new pump was fitted, was the system drained and refilled? If so, was new inhibitor added? If the system has been filled with new water with no inhibitor, you could be getting corrosion which is producing hydrogen - hence the need for frequent bleeding.

As others have said, you need to determine whether it's air or hydrogen coming out when you bleed. Collect some in a jam jar, and put a match to it. [You won't demolish the house in the process]. If hydrogen, it will burn with a blue flame.

[Dave Liquorice]

Remembering tha hydrogen is lighter than air so have the jar over the vent, though at an angle to cath the gas as it squirts out and keep it inverted. B-)

[Hugo Nebula]

...

The ballcock on the header tank has seized shut, and the water is below the inlet, so the pump's been sucking air through it. D'oh! So filled the tank up for tonight, and off to Wickes tomorrow.

[SteveW]

This happened to me last week. I took a radiator off the wall for decorating and then replaced it, allowed it to fill and bled it. Some time later my son reported that the pump upstairs was making odd noises. I checked and switched off - too late, the pump was wrecked from running dry. I checked in the loft and the header tank was full and the feed pipe is only 12" from the pump, yet there was no water there. It turned out that the bottom 4" of the feed pipe was blocked by sand that can only have come in with the water supply (the system has been virtually entirely re-plumbed, flushed and running fine for the last 9 years)!

I still can't see how sand could build up in the bottom of a vertical feed pipe when the flow pipe that it tees into is totally clear.

SteveW

[SteveW]

I bleed with the pump on or off (each room is independently doing its own thing, so the pump can start at any time and if you're downstairs, you won't hear it if it's only supplying one or more upstairs rooms). I bleed the system every autumn, but it's only a check really, as nothing ever comes out. It used to and the system was full of awkward airlocks, but some re-plumbing and a proper air separator ended all that.

SteveW

[Jim K]

that's a helluva lot of corrosion happening hellish quickly!

thinking back to basic school chemistry hydrogen "pops" i.e. it explodes when a lit match/spill is introduced into a test tube /jam jar?

& isn't the flame invisible unless mixed with oxygen in which case it's yellow/orange?

(I know it's academic now)

Jim K

[Man at B&Q]

No need for faffing, just put a lit match in the "air" stream when bleeding.

MBQ

[polygonum]

Quite. Whoever messes around with jars and so on?