trapped air preventing hot water in en suite.

[themoog]

hi. I am new to this forum so first I will say hello.
I live in a bungalow with a hot water cylinder in an airing cupboard next to one bathroom. The shower in the bathroom runs off a pump at the base off the cylinder. The pump is fitted with non return valves before it and there is an Essex valve in the top of the cylinder.
The tank also supplies another bathroom with hot water at the other end of the house.
There is also a pump in the ceiling above the second bathroom that ups the water pressure to hot and cold in this bathroom as it is about 20 m away from the cylinder. This pump has air vents just before it.
Every two weeks or so the hot water to the second bathroom becomes unavailable due to air being trapped in the hot side of the pump and I have to switch the pump off and run the hot water until the air comes out.
why is this happening? It only started doing it after I fitted the pump by the cylinder but I had the non return and Essex valves fitted in an effort to stop this from happening. The system is drawing air in from somewhere but I'm out of ideas.
Any advice is welcome.
Ian

 

[Old Account]

Hi Moog,

Welcome along. Perhaps you could upload few pictures here so the other engineers will have a better idea of your installations ?

Me personally wouldn't install the non returns before the pump.

regrads,
Ron

 

[Stigster]

Pump manufacturers tend to be very fussy about following installation instructions to the letter. There are all kinds of ways you can plumb them in and have them work but air ingress through incorrect connection to the hot distribution of the cylinder is a common problem. I'm not saying your pump is installed incorrectly but as Matchless says, some photos of the setup and how the various pipes connect would really help.

 

[rpm]

Couple of things. ....
Does the 1st pump also send water to the 2nd pump which is 20m away and around 2.5m higher than the 1st pump?
Have I got this right?

 

[themoog]

Firstly let me thank you for your replies.
No, the pumps are separate. One supplies one bathroom and the other supplies the en suite.
The lack of HW to the bathroom next to the airing cupboard happened only a few minutes ago. I heard a different tone from the pump which meant it was cavitating so I switched it off with the water still running so the air could pass through it then switched back on. All ok.
the system is drawing air is drawing air in somewhere and its getting more frequent.
As for pipe connections, the pumps have hot and cold supplies to the inlets - pretty standard really. When I get chance I will try and post some photos.

 

[Chuck]

I'm visualising something like the attached diagram. If I've interpreted what you wrote correctly, it's possible that either (a) pump 1 is trying to pull hot water faster than the Essex valve can replenish it or (b) the air vent or pump 2 are not suitable for negative gauge-pressures and/or are leaking air.

If my diagram is right I'm surprised the system works at all so let us know how your system differs from it.

EDIT: Changed diagram to add the antigravity loop that should be there.

 

[ShaunCorbs]

anti gravity loop should be on pump 2 also too far from cylinder

 

[themoog]

just to clarify- the pump above the en suite was there when I bought the bungalow. As it is so far from the HW cylinder there would be no hot water pressure.
I installed the pump to supply the shower in the bathroom next to the airing cupboard as there was low pressure at that shower. This pump is installed as per instructions that came with it- fed from the top of the cylinder (via Essex) and cold water tank in loft, through non return valve, through pump and to shower. There is no gravity loop (I'm not a plumber but a plasterer..) and I'm not even sure what that is..
The pump over the en suite is fed via same Essex valve and cold tank,past auto air vents, pump, then shower/basin/ toilet as it did when we moved in.
I have a friend who is a top plumber install the Essex and non return valve for me in an effort to stop this happening so I will give him a call to see what he thinks.
It's baffling me and I am usually pretty good at fixing problems.
The above diagram is just about correct.
I understand that bubbles of air are in the top of the cylinder and the Essex valve protrudes down further to prevent the air getting in, however, the tube on the valve is only about 5" long- surely they should go a bit deeper into the tank?

 

[cr0ft]

Where is the cold water storage cistern that feeds the hot water cylinder and how big is it? If it's not a part of the hot water cylinder (i.e. built into the top of it) then what diameter of pipe connects this cistern to the cylinder?

In addition, what side does the cold feed pipe to the hot water cylinder leave the cistern from? The same side as the float valve comes into the cistern or the opposite side?

My bet is that this cistern and/or the cold feed isn't big enough and the pumps are running dry.

 

[themoog]

The cold cistern is in the loft 8m away and about 2m above the hw cylinder.
As for the inlet/outlet pipes they are on opposite sides.
The pumps are not running dry I believe- It's when they are first started I can hear the one by the cylinder has no hot water in it as it screams like mad..
The pump over the en suite just seems to gather air in it over a period of a week.

 

[Chuck]

The cold cistern is in the loft 8m away and about 2m above the hw cylinder.

Okay, so my sketch, which was supposed to show a Fortic-type combined cylinder seems wrong on a couple of points. Your cold tank level is supposed to be above pump 2, which makes more sense. Also, I now suspect that you aren't sharing an outlet from the HW tank but have separate ones. Also by 'Essex valve' I think you meant 'Essex flange'. I on the other hand meant 'ball valve', of course.

I don't seem to be able to edit or delete my post to fix it, sorry.

 

[JVTrades]

If both showers are running off of one essex flange with the higher pump teed off of the drop to the one at the bottom of the cylinder as in the illustration above then you'll be drawing hot water out of the supply pipe work to the higher pump too. Both pumps should have their own hot and cold water supplies. Supply pipe work to the pumps should also be one diameter bigger than than the drawer off, especially with the one furthest away otherwise you risk the pump moving more water than can be supplied

Pictures would help

 

[DerekJB]

Hi Having read all of the above posts. do you mean surrey flange with both outlets at the top of the cylinder? one vertical and one horizontal, as I can't see how you could use an essex flange on a copper cylinder, if its plumbed in correctly the horizontal one should feed the lower pump and the top one feed the one in the loft, the recommendations by companies like stuart turner etc don't recommend check valves on the pump pipe work.
its possible every time you use the kitchen tap the pipework to the pump in the loft can drain back down due to capillary action i.e. the flow draws the water as it passes the T joint. this is the area you would need to use a check valve/non-return valve as it would stop the draining of the pipe work. but as said before, pictures would be good.
hope this helps.

 

[cr0ft]

Maybe drop us a couple of photos showing the setups in the loft and airing cupboard. We can probably advise you from there.

What's the volume of the cold water storage cistern and what's the diameter of the pipework connecting this cistern to the hot water cylinder? 22 or 28mm?? For 2 pumps you are going to want this to be 28mm. If the pipework from the cistern to the cylinder is too small (which it's likely to be) then this causes a partial vacuum upstream of the pumps (i.e. in the cylinder). This is then rectified by the pumps sucking air down the open vent and into the pump supply pipework themselves.

If there's no automatic air vent on the pump in the loft then this definitely supports my theory, especially as you say it builds up over a week or so.

If the pump has no hot water in it then it is running dry, they are one and the same thing

 

[Gasinspect]

yes, would agree you need 28mm feed and full bore valve from cold water cistern into cylinder, especially in bungalow with cw cistern not far above the cylinder. why did you not go for unvented cylinder? coming down in price and less trouble than pumps.

 

[themoog]

sorry if its a bit confusing as I'm not a plumber..
pump 1 (at the base of the cylinder) is teed off the hw outlet from the Essex/surrey flange at the top of the cylinder. The hw was already supplied to the bath/shower that way, it just had no pump.
pump 2 (above the en suite) was already there and is also fed by the flange at the top of the cylinder. Pump 2 has auto air vents just before it.
the only way I can imagine air getting in is via the cold water tank or if the auto vents are knackered.
All this started happening after I put pump 1 in place so its definitely something to do with that. It's doing my head in as the wife is constantly moaning about it..