Air in Shower system?

[Sangster]

I have a 2-bar shower pump mounted at the base of the hot water cylinder on the same floor as the shower. 22mm pipes go from the pump to the shower via the attic. A Surrey flange is fitted at hot water feed at the top of the cylinder. This system worked well for many months but has developed a problem. The pump momentarily stops during operation. After each stop, the shower runs cold for a second or so before the hot water arrives again. Also, when the shower is switched on for the first time it runs cold at reduced pressure for 5-10 seconds until the hot water arrives and the pressure visibly increases.
It seems as if air is entering the hot water circuit somehow causing the pump hot water flow sensor to drop out. The initial running cold seems to suggest extra resistance in the hot water circuit due to air having to be pushed through it. But I'm just guessing. I have inspected the pump hot water impeller and it looks fine. The filter is clear.
Does anyone have an idea if this cou;ld be due to air and if so, how is it getting into the system?

 

[seco services]

when this happens is their still flow from the hot taps.

 

[Sangster]

I was going to say that the hot water from the taps remains unaffected, however I just checked it and although there is no change in hot tap flow when the shower is first turned on, when the shower cuts out there is a very small reduction in hot tap flow. Very minimal though.

 

[seco services]

when you say reduction is that cause the cylinder water is low and thats just the water left in the pipe to the tap,

sounds like your cylinder is not filling quick enough to what the pumps taking.

reading back over your post you mention the flow switch,
you can operate the flow switch by using a magnet on the pump outlet.
run the magnet up the outlet and it will lift the flow switch
try this see if the pump cuts out.

is it the same amount of time when you use the shower that the pump will cut out ? ie after a 10 mins on etc.

 

[Sangster]

As mentioned, the hot tap flow mimics the interruptions in the shower but to a vastly smaller degree. In fact if you werent watching for it you probably wouldnt notice the hot tap pressure change.

The shower problem can occurr at any time. I have not noticed that it starts after a certain time. Typically what happens is that the shower runs cold for 10-15 seconds after first swirch-on Then the pressure visibly increases and the water is hot. Then the problem starts, the pump stopping intermittantly for less than a second before restarting. A pulse of cooler water is felt immediately following each interruption. Also....and I should have mentioned this earlier...It is much worse when the boiler is off, ie when the cylinder may not be completely full.

Regarding the flow switch, I can force the pump ON by placing a magnet against the actuator. Not sure what this prioves though. I have looked at the actuator float, and it is moving freely. I assume that as air pockets reach the flow stitch, this drops down, stopping the pump. However these air pockets must continue to move up the pipe away from the switch, otherwise the pump would not restart.

 

[seco services]

can,t see it beening the cylinder running low as you would notice the tap flow decrease long before the shower. as the surrey flange is about 6" longer.
have you tried bleeding all the hot pipework from cylinder to shower ?

 

[Richard C]

• What pump do you have fitted?
• What size is the pipe work from the hws & cws tanks to the pump?
• What type of isolation valves do you have in this pipe work & elsewhere in the system?
• What is the distance between the bottom of the cws tank & the shower head?
• What is the distance between the bottom of the cws tank & the up & over pipe loops to the mixer?
• Do you have air vents fitted in the top of these loops?

 

[Sangster]

There is one bleed valve in the hot water pipe in the attic. It is close to the highest point in the pipe. Bleeding this during a shower sometimes seems to help but not always and the problem still returns next time the shower is used.

The pump is Wickes own label. I think 2.5bar with brass impellers. Looks identical to a Watermill pump. The hot and cold pipework is 22mm plastic except for the short section from the hwc to the pump which is 22mm copper.
There are isolation valves in the pump outlets and in the hot water feed from the hwc. Not sure what type they are.
The hw from the cylinder drops down to the pump and then vertically up into the attic, across the attic floor and down to the mixer. The distance is about 20 feet plus the vertical bits.
The cold water has to go down from the hw tank, probably about 5 feet plus the vertical run to the pump inlet. Then it runs from the pump alongside the hw pipe. As mentioned I had a bleed valve fitted at the top of the hw pipe. There is no bleed valve in the cw pipe.

By the way, many thanks for trying to help. Seems like it is not a simple problem though!

 

[seco services]

what makes it worse is you say it was ok now it isn't.

just out of chance what is the cylinder stat set to ?

 

[Sangster]

The shower system was installed more than 3 or 4 years ago. Immediately after this the installer had a lot of difficulty getting air out of the system and he had to return several times. On these occasions the water flow stopped altogether and the shower didnt work at all. Once fixed though we had no further trouble.
Last Summer the hwc sprung a leak and and had to be replaced. The current problems started a few months later. At first the only issue was the initial switch-on cold water and lower pressure for a few seconds until the hot water arrived. We didnt see this as a problem. Then, a few months later the pump became intermittant during operation as it is now.

The cylinder thermostat is set to 60degC.

Other observations that may or may not be relevant;
The valve in the cold water feed to the cylinder is jammed. I cannot move it and so dont know where it it set to (I haven't tried to force it).
The shower mixer valve may be furred up because the button that allows the temperature to be set above 38degC no longer works freely. Otherwise it is okay though.
We have very hard water.
When the shower is turned off, there is a sucking sound as though air is being drawn in through the shower head.

 

[seco services]

When the shower is turned off, there is a sucking sound as though air is being drawn in through the shower head.

i would try a non return valve on the hot outlet from the pump

 

[Sangster]

Sounds like a plan. Except that the pump instructions say;

"Do not fit non-return valves in the inlet line to the
pump. The pump must be able to vent back to the
supply tank"

Therefore is it okay to fit a check valve in the pump outlet?

http://www.screwfix.com/prods/56234/Plumbing/Brassware/Comap-Double-Check-Valve-DZR-22mm

 

[Richard C]

You haven’t said;
• What is the distance between the bottom of the cws tank & the shower head?
• What is the distance between the bottom of the cws tank & the up & over pipe runs in the loft to the mixer?

You may have several factors that are making the system marginal even when newly installed but being new but it coped & soldiered on once the air was bled from the system. As the system ages, it gets furred up, valves get stuck (possibly not fully open)
& if the loft pipe runs or the shower head are less than 600mm below the bottom of the cws tank, you could potentially be in a negative head situation. You need a flow rate of around 1 litre/min on both h&c supplies at the shower head with the pump switched off & if they drop below this, it maybe enough to prevent the flow switches kicking in.

It’s possible that the mixer valve is no longer sealing when turned off, maybe faulty or non existent nrv’s hence the sound of air sucking back through the showerhead. Not so important on the cw pipe but you should still have a vent at the top of the loop. Fitting a nr valve on the hot pump outlet as seco suggests is OK & may help but if the system is already restricted, it may actually make things worse!

 

[Sangster]

The cold water feed from the tank is about 60cm above the highest point in the pipes from the pump. The shower head in its highest position is about 1m below the cold water feed.

The pump always switches on when the shower is turned on. It just has these momentary interruptions which seem to be in the hot supply since the shower momentarily runs cool. It is usually possible to have a perfectly good shower despite these, and sometimes it hardly happens at all. However, this is not always the case and if the hot water cylinder is not full, for instance if the dishwasher or washing machine has been on and the heating pump turned off, then the intermittancy in the shower is much worse to the point of being unusable.

I agree that the mixer is probably scaled up. It does control the temperature okay though. Interestingly, adjusting the temperature setting can sometimes either induce or temporarily clear the problem.

 

[seco services]

Sounds like a plan. Except that the pump instructions say;

"Do not fit non-return valves in the inlet line to the
pump. The pump must be able to vent back to the
supply tank"

Therefore is it okay to fit a check valve in the pump outlet?

http://www.screwfix.com/prods/56234/Plumbing/Brassware/Comap-Double-Check-Valve-DZR-22mm[/QUOTE]

thats what i said on the outlet from the pump.

also you say about the hw cylinder. it will always be full with heating pump on/off, taps on/off what ever as the cws is supplying it constant.

and if your cylinder wasn't filling quick enough then your taps would be first to get air or no flow.