Hot Water System Appears Airlocked

macgrub

Hi,

Basically, any time my immersion has been working (either manually or during the night ), my hot water system appears airlocked. When I turn on my shower, very little water comes out and the pump that supplies it is very noisy (sounds like it's running dry). The only way I rectify it is by turning on the hot tap in the bathroom, or kitchen, fully. It splutters a bit and a full flow of hot water eventually flows (and the pump sound returns to 'normal' ). This happens every day and I was wondering if anyone had any ideas.
Also worth mentioning, when I clear out the what appears to be an air-lock each day, the hot water is runs fine. It's just after I have the immersion on.
Thanks in advance.

ART6

macgrub wrote: »

Hi,

Basically, any time my immersion has been working (either manually or during the night ), my hot water system appears airlocked. When I turn on my shower, very little water comes out and the pump that supplies it is very noisy (sounds like it's running dry). The only way I rectify it is by turning on the hot tap in the bathroom, or kitchen, fully. It splutters a bit and a full flow of hot water eventually flows (and the pump sound returns to 'normal' ). This happens every day and I was wondering if anyone had any ideas.
Also worth mentioning, when I clear out the what appears to be an air-lock each day, the hot water is runs fine. It's just after I have the immersion on.
Thanks in advance.

It sounds like either the immersion heater is set to too high a temperature, or/and the vent pipe back to the attic header tank is blocked, possibly by being immersed in the water instead of being above it.

macgrub

ART6 wrote: »

It sounds like either the immersion heater is set to too high a temperature, or/and the vent pipe back to the attic header tank is blocked, possibly by being immersed in the water instead of being above it.

Thanks for the reply ART6. I remember an electrician adjusted the immersion to 60 degrees or so. Maybe it's still too high?
I just checked if the expansion pipe was submerged and there is plenty of space between it and the water in the storage tank. Next thing is to check if that expansion pipe is blocked? Any suggestions on how to do this?

ART6

macgrub wrote: »

Thanks for the reply ART6. I remember an electrician adjusted the immersion to 60 degrees or so. Maybe it's still too high?
I just checked if the expansion pipe was submerged and there is plenty of space between it and the water in the storage tank. Next thing is to check if that expansion pipe is blocked? Any suggestions on how to do this?

The immersion heater is just a wild guess -- the possibility that if it was set to "sink" and its thermostat was either too high or stuck closed then the water in the top of the hot water tank could be getting too hot and releasing vapour into the system, thus creating an airlock. Having said that I have never known it to happen, but am prepared to accept the possibility that it could. After all, there has to be some reason why the problem only exists when the immersion is on.

Where the vent pipe is concerned, that's another wild guess, but it might be possible that if it's blocked or not venting properly then when the hot tank cools down with the immersion off the contraction of the contents might be drawing air in but not releasing it again through the vent. It might even be that there is an airlock in the system all of the time, but for some reason the immersion worsens it. One way of checking the vent is to connect the cold and hot taps in your kitchen and open them both slightly. That will force mains water back through the system and cause it to escape through the vent pipe and back into the header tank. The latter might overflow down its overflow pipe, but that won't matter for a minute or two. If nothing else, doing that will ensure that there isn't any residual airlock or blockage anywhere.

If your kitchen tap is a single spout mixer type, then stick a plastic bottle over the spout and again turn on both taps.

macgrub

ART6 wrote: »

The immersion heater is just a wild guess -- the possibility that if it was set to "sink" and its thermostat was either too high or stuck closed then the water in the top of the hot water tank could be getting too hot and releasing vapour into the system, thus creating an airlock. Having said that I have never known it to happen, but am prepared to accept the possibility that it could. After all, there has to be some reason why the problem only exists when the immersion is on.

Where the vent pipe is concerned, that's another wild guess, but it might be possible that if it's blocked or not venting properly then when the hot tank cools down with the immersion off the contraction of the contents might be drawing air in but not releasing it again through the vent. It might even be that there is an airlock in the system all of the time, but for some reason the immersion worsens it. One way of checking the vent is to connect the cold and hot taps in your kitchen and open them both slightly. That will force mains water back through the system and cause it to escape through the vent pipe and back into the header tank. The latter might overflow down its overflow pipe, but that won't matter for a minute or two. If nothing else, doing that will ensure that there isn't any residual airlock or blockage anywhere.

If your kitchen tap is a single spout mixer type, then stick a plastic bottle over the spout and again turn on both taps.

If I have a twin-impeller centrifugal pump supplying the hot water, and cold from the storage tank, around the apartment. Would the pump be safe if I was to perform that exercise of connecting one tap to another?

ART6

macgrub wrote: »

If I have a twin-impeller centrifugal pump supplying the hot water, and cold from the storage tank, around the apartment. Would the pump be safe if I was to perform that exercise of connecting one tap to another?

You didn't say in your OP that you had a pump, but it might be it that is the problem. If the pump is OK then an airlock would seem a remote possibility, but it may be that the hot circuit impeller is worn or something and simply doesn't like water that's too hot.

Is the pump continually immersed (ie. is it located below the water level in the storage tank)? If it's only just below the tank water level then I would suspect that the hot circuit impeller is too worn to prime properly, and the hotter the water is the worse it gets. In that case opening several hot taps might be sufficient to get a good flow through it and cause it to pick up. That might be why the immersion seems to be affecting the flow.

All of this, I'm afraid, is pure guesswork though. What's the make and model number of the pump?

macgrub

ART6 wrote: »

You didn't say in your OP that you had a pump, but it might be it that is the problem. If the pump is OK then an airlock would seem a remote possibility, but it may be that the hot circuit impeller is worn or something and simply doesn't like water that's too hot.

Is the pump continually immersed (ie. is it located below the water level in the storage tank)? If it's only just below the tank water level then I would suspect that the hot circuit impeller is too worn to prime properly, and the hotter the water is the worse it gets. In that case opening several hot taps might be sufficient to get a good flow through it and cause it to pick up. That might be why the immersion seems to be affecting the flow.

All of this, I'm afraid, is pure guesswork though. What's the make and model number of the pump?

The pump is a Grundfos STC .
I was doing a little bit of research online and found a few schematics of systems similar to mine. Then, I found the manual to my pump and I noticed that my heating system is lacking a Surrey flange on the output of the Hot-water cylinder. Might this contribute to my problem?

ART6

macgrub wrote: »

The pump is a Grundfos STC .
I was doing a little bit of research online and found a few schematics of systems similar to mine. Then, I found the manual to my pump and I noticed that my heating system is lacking a Surrey flange on the output of the Hot-water cylinder. Might this contribute to my problem?

If the pump is not far below the water level in the header tank then yes, it's quite possible that the absence of such a flange is the problem. The sole purpose of those flanges is to ensure that the pump draws hot water from below the top of the cylinder rather than air bubbles that might be passing though the top. Normally, if there is sufficient head between the attic tank and the top of the cylinder that wouldn't be an issue as there would be too much water pressure from the head, but with a low head the pump could be drawing in air from the vent, and a Surrey flange would prevent that.

In responding to your post I had assumed that this was a new problem, which is what happens when you make assumptions before engaging the brain! Is it a new problem or one that's always existed?

macgrub

ART6 wrote: »

If the pump is not far below the water level in the header tank then yes, it's quite possible that the absence of such a flange is the problem. The sole purpose of those flanges is to ensure that the pump draws hot water from below the top of the cylinder rather than air bubbles that might be passing though the top. Normally, if there is sufficient head between the attic tank and the top of the cylinder that wouldn't be an issue as there would be too much water pressure from the head, but with a low head the pump could be drawing in air from the vent, and a Surrey flange would prevent that.

In responding to your post I had assumed that this was a new problem, which is what happens when you make assumptions before engaging the brain! Is it a new problem or one that's always existed?

This is a problem that has always existed (or since I've moved in).
The distance between the cylinder and the foot of the storage tank is about 6 - 8 inches. I'm not sure if that would be adequate space?

(just to clear up, I'm in an apartment. The storage tank is above the hot-water cylinder - all in the one hot-press. The shower/water pump is beside the cylinder on the floor. I'm sorry if I'm confusing the situation )

ART6

macgrub wrote: »

This is a problem that has always existed (or since I've moved in).
The distance between the cylinder and the foot of the storage tank is about 6 - 8 inches. I'm not sure if that would be adequate space?

(just to clear up, I'm in an apartment. The storage tank is above the hot-water cylinder - all in the one hot-press. The shower/water pump is beside the cylinder on the floor. I'm sorry if I'm confusing the situation )

Don't worry about confusion -- I should have asked the right questions to start with rather than just jumping in!

Given that the header tank is immediately above the cylinder in a hot press, there is nothing you can do to increase the head pressure (or the height of the tank), so we can discount that. That leaves us with the problem that the hot water end of the pump will not deliver water to the shower properly when the immersion is on, but will do so if a hot tap is opened. The difference there is that the flow needed by the shower will be much less than that passed by a fully open hot tap, and so the flow of water from the cylinder to the pump will be correspondingly much less.

When the immersion is on it is probable that some air bubbles are created against the immersion element, and normally these would rise up the vent pipe and be released above the header tank. However, assuming that the pump draws from the same pipe immediately above the cylinder, I would think it entirely probable that air is collecting in the pump suction pipe and that with only the shower on there is insufficient flow to dislodge it. There only becomes enough flow to do so when a hot tap is opened. With such a small head pressure (the height of the header tank above the pump suction connection) that doesn't sound surprising.

That being so, I would say that your theory of needing a Surrey valve is correct. Alternatively, if you can do it, you could refit the pump suction pipe so that it slopes downwards from the tee that connects it to the hot water riser pipe. That would also stop air from collecting in it.