Air/gurgling noises in airing cupboard pipework

[BuckSFinUK]

Hello all,

I've spent several hours browsing through previous posts to see if I could get some direction, but none of the suggestions in them has allowed me to remedy the problem.

The system is open vented, gravity fed with a Potterton Suprima combi boiler, unknown (no label) hot water cylinder/immersion heater, Grundfos Selectric pump, Drayton 3 way actuator/valve and 9 radiators.

Three weeks ago I drained down the heating system, and installed TRVs on all of the radiators except for the one in the hall where the thermostat is mounted. The water in the radiators wasn't dirty when I drained it down and I used a cleanser, flushed the system several times and filled it using an inhibitor. I bled all the radiators, tested all the new TRVs and everything was working as expected. So far so good.

Except now when the hot water program kicks in morning and evening, the pipework between the pump and the hot water cylinder/immersion heater makes all kinds of gurgling noises for several hours. I've checked to make sure the Feed and Expansion tank is filled and functioning properly, and have repeatedly bled the radiators, pump and the bleed point on the short vertical riser above the 3 way valve. These are the only bleed points I can find in the system.

My questions really boil down to these:

-Are there any other bleed points I should be aware of?

-Should I 'crack the nut' on the top of the cylinder/immersion heater to release any air potentially held there?

-Several earlier posts seemed to point at a failing 3 way valve/actuator as the culprit for these symptoms. Does that sound reasonable? It seems somehow suspect to me that the valve would choose to fail just when I changed out the radiator valves, but I suppose it's possible.

Any direction you could give me would be greatly appreciated.

 

[gas4you]

First thing I would suspect is an air lock. Is there an air bleed point next to the hw cylinder off the flow to the cylinder coil?

I take it you have checked that the f&e tank is full of water?

Next thing to suspect could be a blocked cold feed pipe where it joins the heating pipe work.

Do a search on here for blocked cold feed

 

[BuckSFinUK]

Thanks for the reply.

There is an air bleed at the top of a short vertical length of pipe that connects to the top of the 3 way valve. I have bled it repeatedly, and usually get small amounts of air out of it. I have opened it more fully on several occasions and let it run for several minutes in the hope it will remove the air but so far no dice.

Yes, the F&E tank is filled to the correct water line and is working properly.

I'll have to do the magnet routine tonight on the cold water feed into the area in question. I'm pretty dubious about sediment or corrosion build up given the heating system was completely replaced 6 years ago and the radiators had pretty clean water in them when I drained them down.

I'm not having any problems with lack of hot (or cold) water or pressure reduction. Could a partial blockage cause the gurgling sound but allow the system to still function fully?

It still seems to me there must be some way to bleed the cylinder/immersion heater, but I can't find any bleed point anywhere on or about it.

Thanks again for the tips.

 

[croydoncorgi]

By this time, air trapped in the system SHOULD have found its way out via the open vent, especially if (as you suggest) it's circulating in the hot pipework connected to the cylinder.

Are you SURE there are no air leaks (INTO) the system. Favourite places for these are pump valves - the stem glands and the unions onto the pump itself, on the inlet side of the pump and other pipework nearby. On an open-vented system, quite large parts of the system will be at pressures BELOW atmospheric when the pump is running, so air can get in via small leaks that don't actually leak (much) water out.

The reason someone asked about a (partly) blocked cold feed was because this can cause air to be drawn down the open-vent pipe when the pump starts up. A way to check this is to hold a jar full of water over the end of the vent pipe and have someone start the system. If the water in the jar gets sucked up the vent, there's your problem!

There's NO connection between the heating water in the cylinder and the water coming out of the taps (unless it's a Primatic type). The hot water side of the cylinder vents automatically via the outlet at the top. DO NOT under any circumstances touch the immersion heater joint unless you plan to remove it!!!

 

[BuckSFinUK]

Thanks for the reply croydoncorgi.

I'll check for leaks around the pump tonight. There are isolation valves above and below the pump so I can take it off and clean the connections which do have some residue showing on the exterior of the pump itself and I suppose could indicate small leaks.

Since I've not removed this pump before, what do you suggest when replacing it after cleaning the fittings? Do I need any plumber's dope (what it's called Stateside) or are those compression fittings? I'm not at home right now so can't get a good visual on those joints.

I'll also try the cold water feed test with the jar tonight and report back.

Thanks again.

 

[JohnD]

you mention repeated bleeding. This might be from air getting into the syst, e.g. a leak on the suction side of the pump; but it could also be gas produced as a result of corrosion of the steel radiators. In this case the water you bleed out is likely to be tinged with black (or brown, which is worse).

Climb into the loft before the system stars running. Find the feed and expansion tank and see how much sediment it has at the bottom. See how deep the water is. Observe the vent pipe which is bent over the top of the F&E. Watch to see if water comes out of this when the boiler and pump start up.

Do you know if the system contains chemical inhibitor; what was added when it was drained and refilled; if it has ever been cleaned out?

edited: too slow

 

[croydoncorgi]

I sort-of assumed that you'd already had bits of the system apart.

If the pump unions are showing leakage deposits on the outside, they're definitely worth a look. In particular, you may find there are FIBRE washers on the 1.5" loose unions connecting onto the pump body. Some pump manufacturers supply RUBBER washers with their pumps. The fibre washers tend to leak, the rubber ones don't! Pump unions, if clean and with the right washers, do NOT need extra sealant or to be 'murdered' when tightened!

The stem seals on the pump isolators need checking too. If the pump isolators are the 'ball' type as opposed to the gate type, change them - they'll probably start oozing as soon as you try to isolate the pump!

 

[BuckSFinUK]

To JohnD,

Thanks for the reply.

The radiators appear in good condition. The water was hardly discoloured when I drained the system and I used a cleanser and put an inhibitor in when I installed the TRVs.

I also completely cleaned the F&E tank when I did the install, taking care that no sediment got into the pipework. I have watched the vent pipe as you describe and no water comes out of it when the system is turned on.

To croydoncorgi,

Thanks for the follow up and direction on the pump isolator fittings. I'll check them tonight when I get home and report back.

Are replacement rubber 1.5" washers for the pump fittings something I can obtain easily at a plumber's merchant?

Thanks again for the feedback.