No cold water coming out of shower, heats up then stops

Hi All,

Thanks in advance for any help. From reading posts, I see you guys like lots of detail. I apologise if this is too much

Problem in a nutshell, is that the shower has stopped giving cold water it seems. If you run the shower with the thermostat set to 'warm', then the water starts powerful, and slowly fades as the water heats up. Turning the thermostat all the way to cold makes it stop completely, turning it all the way to hot, it speeds up (But is VERY hot). Shower is fed by a Monsoon Twin 3.6bar pump by the hot water cylinder upstairs, shower is also upstairs. The pipes appear to go into the loft along, and down to the shower (rather than udner the floor). There are several stop cocks by the pump, and in the loft, and have tried to make sure they are all on.

This started occuring after a plumber visit to fix a broken heating pump. That was replaced, and central heating fixed, although I asked whilst he was here he could look at the cold water tank, as the feed constantly drips into the tank, and when we go on holiday for a week, it start going down the over flow to outside. The ball cock and mechanism were very scaled up, and looked ancient, so he replaced them. However, I started hearing a dripping a couple of days later, and noticed there was now a leak on the OUTSIDE of the tank in the cold feed, and water was dripping and making a mark on the ceiling. There was a stop cock a couple of feet from the cold feed, before the leak, so I turned this off, and called the plumber back, he make it a couple of days later. Whilst I was at work, my wife and a friend had a shower, and used up all the water in the tank and the shower stopped. After plumber had been, everything switched on again, tank filled up, but shower not giving cold.

So, my first thought is air in the cold watre pipe, but surely that doesnt make sense, as the twin pump is coming on when the hot is called for, so wouldnt that also pressurise the cold, and get the air pushed through easily? So i'm wondering if totally by coincidence the shower thermostat mechanism thingy (technical term) now has a fault, and isnt letting the cold come through?

The cold water tank has a vent pipe over it, as does a smaller tank, which I assume is the heating header tank. I'm not masively familiar with these things. Our hot water is gravity, central heating is pumped. Not relevant i'm sure.

Is it possible to get an airlock, that cant get pushed through, even with a 3.6bar twin shower pump??? When it runs, doesnt it pump both sides, or are they actually separate.

Many thanks in advance for any help.

Kevin.

thermostat mechanism thingy .... I would know it as a thermoscopic actuator

Insufficient water storage is common where shower pumps are fitted. It could be that when the tank ran dry that some debris was dragged in and is stuck in the pipework.
Theres often a filter [and a non return valve] on the inlet to the shower that could be blocked
Perhaps this debris may have affected the function of a flow switch?
Perhaps a valve was closed and not re-opened?
Does the pump sound any different than it used to?

Hi,

The pump doesnt sound noticeably different. Looking at the website for Monsoon shower pumps, it appears they may have a strainer on the inlets both sides. I suppose its always possible that something got dislodged, and this made its way down the pipe to the shower pump, but I would still expect something to get through. There is literally no cold coming through at all when the hot water is running hot, not even a dribble. Turning shower all the way round to cold it is totally stopped, like it is off. I'll recheck all the stop cocks, but pretty sure I've already made sure.

Cheers,
Kevin.

Ok, I phoned the guy who installed the shower a year or so ago, and asked him if he had any ideas. He seemed to think it could still be an airlock in the cold, sincfe the tank had run dry. He said if I felt up to it, I should isolate the inlet and outlet valves on the pump, disconnect the inlet, then open the inlet valve a tiny bit with a bucket under it, which should then purge any air that is somehow in that pipe. It doesnt seem possible, being a simple 'along and down' type arrangement from the water tank, but needs to be eliminated I guess.

So, I checked the stuart turner website, and the diagrams of the 3.0 bar twin on there is slightly different to mine. I have no nuts, its all push fit on both end of the flexible connecting hose. It looks like there is just two screws, holding down what they call a 'manifold' on to the housing, and under there is the strainer and an O-ring.

The pump had the year 1997 on it, so I guess its changed since then, and incrases the likelihood the strainer needs cleaning anyway. Has anyone ever taken this 'manifold' thing off before? Anything I need to beware of? The last thing I want is to do this, and then connect it back up and it leaks.

Basically, how easy is it to clean these filters, should I attempt it myself?

Cheers,
Kevin.

Ok, its all sorted.

Just in case someone comes across this thread whilst searching for a similar problem, I did just need to disconnect the inlet to the pump. As soon as I did, there was lots of hissing as the air escaped. Then connected it all up, lots of sputtering from the shower, but cold now working. Hurrah!

Can't believe the pump couldnt push it through, but there you go. Guess that's why they call it an air 'lock'.