Air block in hot water system

FrankGrimes

I’ve got some majorly bad air blocks in my hot water system.

The hot water tap in the utility room is worst affected and only a dribble comes out. There is a downstairs toilet and the hot water flow in the tap in there is fine (no kitchen yet – to follow with extension). There is a bathroom with taps on sink and bath and separate pumped shower upstairs. Flow in both those taps is fine (though it was bad for a while). Shower was fine, but has now dropped since I emptied the system yesterday.

There is a washing machine and dishwasher fed off the hot water feed that runs to the hot water tap in the utility room. This feed is half inch though I’ve been told it should have been ¾ inch to avoid a drop in pressure when appliances are on (if they did need hot water), but don’t get me started on the plumber who put it in! Pressure in both the hot water feeds branching off this pipe before it gets to the utility room sink is very strong, though it drops dramatically in the hot water tap.

Last week I turned off the mains feed and disconnected the hot and cold taps under the sink in the utility room and connected a flexi hose from cold feed to hot feed. I then reopened the mains with the intention being that the mains pressure would blow the hot water back up to the overflow pipe flowing into the cold water tank in the attic, and that this would clear any air blocks.

The pressure in the hot water tap in the utility room was fine after this. However, it dropped back to a dribble after two days, so I emptied the system last night thinking no water means no air can get blocked, but no joy, and this has caused the shower pressure to drop.

Any ideas how I can fix this? Should I have the taps around the house open or closed when blowing the mains water into the hot water system? Should I have the taps open or closed when I’m refilling the system after emptying it?

Thanks

Judean Reg

Try turning on the tap in the bath and holding you hand over the outlet. Then when the pressure builds up, release your hand and try and blow the air out this way. It might help.

FrankGrimes

thanks - I should have mentioned that I tried that already and had no joy.

FrankGrimes

If anyone has any ideas on this one it'd be much appreciated. I bought a drain blocker thing at lunch which is kind of like a plunger but has a handle to pump up and down on it. It has a small fitting that I'm hoping I can put over the half inch pipe to suck the air out of it, but not holding out much hope.

Would be great is anyone knows the normal causes (e.g. should taps be open or closed when re-filling system) or airblocks and best approach for clearing them.

Corkey123

Franks

Just a couple of comments first.

I would connect the washing machines and dishwasher to the cold source and let the appliance deal with heating the water. This will reduce the draw on the prtessure of the hot source as well as the hot water in the tank. half inch is quite enough for these as it is likely that the source of the hot tank, although initially 3/4 will come down from the bathroom as 1/2, changing to 3/4 is pointless.

As the hot water leaves the hot tank it rises up to the attic and then down to the bathroom via a 3/4 pipe. This is the high point in your hot water system and this is were your air is located. If you emptied your storage tank at some time recently it is likely that some air got it to the hot system by mistake and the result is spluttering and low pressure.

Immediately above the hot tank in the attic there should be a release valve or a bleeding valve to allow air out of the system. Have a look,

I'm making a lot of assumptions here so don't be too critical

FrankGrimes

Thanks for the reply Martin.

I don't have the disher connected to a hot feed, but have the branch in place in the hot water pipe just in case it was needed. I have the washing machine hooked up to both hot and cold, cos we don't use much hot water as there is only two of us, so might aswell give the washer heated water that would otherwise be wasted. Will change to cold only when usage changes.

Last night I got a flexihose and fed mains water into the pipe feeding the hot tap in utility room. I left this on for 10 minutes. Cold water tank in attic was filling up to almost overflowing (water coming in faster than overflow pipe could get it out). I always thought that thought that there was an overflow pipe that ran from the hot water cistern to the attic, where it hangs over the cold water tank, to let excess hot water spill out into the tank.

However, I do have a pipe thats curved over the cold water tank and sitting over it, but no water was coming out of this. Instead, it seemed that the pipe heading up from the hot water tank (which has a cut-off handle on it) was actually feeding into the bottom of the cold water tank. This has confused me. Plumber was a cowboy so no idea what way he set it up. There was a red expansion tank before but I don't see it anymore.

When you say "As the hot water leaves the hot tank it rises up to the attic and then down to the bathroom via a 3/4 pipe." why does the hot water run up to the attic?

I also hooked the mains feed directly to the hot water tap, and this gave a steady flow, though not as good as through the actual cold tap, so it may be a problem with the hot water tap.

Anyways, net result is I have a better flow in the hot tap now, though its not ideal, we might just get away with it. And the flow in the shower is much improved, actually better than it ever was so thats good, but I still want to understand how my setup works to solve similar problems in the future.

Thanks again.

Corkey123

Frank

When you say "As the hot water leaves the hot tank it rises up to the attic and then down to the bathroom via a 3/4 pipe." why does the hot water run up to the attic?

the pressure of the cold water storage tank applied to the cylinder provides pressure to allow the water flow to the attic, where with the help of gravity it gains further pressure, this is more efficient than taking the hot water from the cylinder and running it under the floors to your bathroom.

Instead, it seemed that the pipe heading up from the hot water tank (which has a cut-off handle on it) was actually feeding into the bottom of the cold water tank. This has confused me. Plumber was a cowboy so no idea what way he set it up

This is as it should be, this is how the pressure is applied to the cylinder.

Using the hose to force water into the cylinder and blow out air sems to have done the trick, but there must be an easier way.

FrankGrimes

Thanks Martin, I kinda get some of it now, though still not clear. Does this sound like a standard setup that I could lookup in a book?

What is the purpose of the second pipe that is curved up and over the cold water tank - is this for excess hot water/air to flow into?

So the first pipe joining the cold water tank to the cistern increases pressure in the hot water system, and the hot water then leaves the cistern via another pipe and goes up to the attic (where it does what?) and then comes back down to the outlets with increased pressure due to gravity?

Corkey123

What is the purpose of the second pipe that is curved up and over the cold water tank - is this for excess hot water/air to flow into?

As you suspect it is used for emergencies where a cylinder malfuctions (maybe due to the immersion going mad or something), this is a release pipe, rarely used but essential.

So the first pipe joining the cold water tank to the cistern increases pressure in the hot water system, and the hot water then leaves the cistern via another pipe and goes up to the attic (where it does what?) and then comes back down to the outlets with increased pressure due to gravity?

Thats about it, by the way Cylinder not cistern