Erratic shower pressure

[mike42]

We had a shower pump installed as part of a bathroom refit around a year ago. The pressure has always been a bit variable so that normally at the start of a shower, the pressure is often poor but after several minutes it improves.

Recently, there seem to be more and more showers whereby the pressure doesn't improve and stays poor for 10 minutes or so. I'm at a loss of how to troubleshoot this and I don't know if its the mixer or something wrong with the pump/tank installation.

The HW tank is particularly large (can't recall the height but about 50% bigger than the one that was there before) and there is a techflow flange at the top (pump is also techflow middle presure one).

With the pump powered off, it seems the hot and cold pressures are about the same. When its on in normal operation, its easy to get a strong pressure of pure cold water but not hot.

Could it be that I need to fit a side flange?

Its a normal hot water tank in airing cupboard with pump on the floor arrangement and cw tank is high up in loft.

Thanks for any thoughts on this.

 

[picasso]

I would start with the filters in the shower valve and the pump if it has them.

 

[mike42]

Thanks Picasso and very interesting that you say that because the "European" builders that fitted it were bordering on the "cowboy" side of professionalism. They did a reasonable job with "first fix" aspect such as plastering/tiling etc but were very poor at plumbing and installing technical items such as the internal geberit WC cistern and expensive glass shower door Perhaps more relevant is that they totally cocked up the Grohe mixer so that it is very hard to actually turn the shower off (you have to try and find a middle point between the main shower and hand-shower to stop either from dripping) plus the temperature control is not fixed propery since it comes off in your hand if you apply the slightest of pressure away from the wall.

Anyway, the point is I could more than believe they chucked the filters in the bin but if they did that, why could that cause this problem?

 

[mike42]

I should have added that they also replaced the HW tank and CW tank in the loft. I know for sure that the plastic "trimmings" you get from drilling the holes in the new CW tank were left in the tank whereupon they filled it up and I was left trying to get them out with a sieve.

Maybe I'm starting to understand the point about no filters in the pump and/or mixer but still can't quite put two and two together in order to understand why that my cause the symptoms described.

 

[picasso]

Perhaps I should have been clearer, the shower valve normally comes with filters built in to the inlets, if the pipework isint flushed before the valve is fitted the filters catch all the debris from the work and slowly block as more flotsam is washed out of the loft tank, pumps sometimes but not always have filters in the inlets, again these can block causing a tail off of pressure/flow.

 

[mike42]

Thanks thats clear but wouldn't that just cause constant poor flow? In our case it seems to change from one day to the next or even after several minutes (usually improving).

 

[picasso]

Its really a case of elimination, start with the tank in the loft are the feeds to the pump clear ? undo the connections to the pump and run full bore into a bucket, does the flow slow down or speed up ? could the non return valves be sticking ? are the filters clear ? try taking the head off the shower hose, try taking the hose off , if you live in a hard water area could the hot water cylinder be choked with lime scale, if there is a gate valve on the feed to the cylinder is it fully open and finally air can cause havoc in a pump, make sure you have followed the manufacturers instructions with regard to clearing air.