Help! Hot water feed to shower not working: how to DIY fix?

[mutterphore]

The only available shower in our house has virtually no hot water coming through. I suspect we've got an air bubble blocking the pipe, from what I've read about on the internet but I might be wrong. Hot water pressure is about nil but cold water pressure is still OK and we can get hot water out of sink taps OK.

Are there any DIY methods to fix this? I've already tried turning on the shower to just cold water and then very gradually turning the dial towards hot, to see if the pressure of the cold water pushed out any air bubble but this doesn't work.

DS1 has incredibly long hot showers twice a day and I think he may have accidentally caused the problem by draining off the hot water tank each time and therefore making an air bubble build up over time. Last night, none of us could shower properly and each of us showers twice a day.

Can't get hold of the builder and his plumber who fitted the shower 18 months ago and know he's very busy anyway. So I'm trying to find a way to fix it myself.

Anyone have any ideas please?

This isn't a power shower by the way - just a basic one run off the gas central heating system.

Wondering if @PigletJohn is still around on MN and could advise - or anyone else for that matter?

What colour is your hot water cylinder?

Take the shower head off so the flow isn't restricted put the hose on the shower floor for maximum head and see if you can flush through if it's a bubble. Clean the shower head if the hot water is lower pressure than the cold, blockages in the shower head could slow the hot right down.

@PigletJohn thanks for coming on to this thread! The hot water cylinder is greeny blue.

@Silverbirchtwo thanks also for your help. That's the one method I've tried and unfortunately, so far, it doesn't work. It could be that the air block is too big and longstanding.

Would draining the hot water tank really cause an air bubble? Surely the used hot water is replaced by cold water, not air?

@ScaredSceptic from what I've read on the internet, I think that the hot water tank draining to near empty and not refilling in time whilst the shower is still being used, can cause an air bubble/block to form in the hot water feeder pipe. I could be wrong about this though as I'm not a plumber, just a mum trying to provide showers for adult DCs and myself.

I've also noticed that when we turn off the shower, there's this really loud bang sound and I think that's also associated with an air block in the pipe.

The shower is downstairs by the way, @PigletJohn and the cylinder upstairs above that room and the water tank in the loft.

If the shower is downstairs, any air bubble is likely to be higher, in a horizontal or looped pipe, likely near the cylinder. As you have a cylinder, there might be a separate pipe to the shower, rather than being teed off the existing hot taps.

when you turn the shower mixer to cold, is the strength of the water jet noticeably more forceful than the hot used to be? Do you know if there is a pressure balancing valve on the pipes, or a pump?

If all the other hot taps are OK, try turning the shower mixer to hot (not mixed with any cold) and leave it dribbling for a while. This may shift the bubble. It's to get flow in the hot pipe, but the water itself need not be hot. Water that is cold is slightly better.

Also, show us a pic of your shower mixer please. It might be thermostatic, or the ceramic type with a joystick, and might have developed a fault.

Has there been any sign of grit, flakes or sediment coming out of the shower? Unscrew the head and rinse it in the sink to see if any comes out.

Yes, it can. The water runs out of the pipe under gravity, and if water is not entering it at equal speed, air will. Though in fact you can't drain a cylinder like that as the draw-off pipe is (almost) always at the top. The air will be in a pipe.

Many thanks, @PigletJohn for your help.

I'm not sure if the strength of the cold water jet is noticeably more forceful than the hot water jet used to be, when it was OK. It might be the same as always but I'm just not sure. Sorry I can't be clear about this. The current hot water jet - when mixer turned just to hot - is very noticeably weaker than the current cold water jet.

I also don't know if there's a pressure balancing valve on the pipes or a pump. Sorry!

Upstairs in the cylinder/ airing cupboard, the workmen who fitted this replacement shower about 18 months ago, helpfully drew a diagram on the airing cupboard door, showing the 2 new pipes coming from the cylinder. One of these is marked, "Low pressure feed to shower downstairs" and is a thinner pipe (as is the other new one) which has a red metal 'turning' tap, as do some of the other pipes - presumably to turn the water flow on and off?

This shower feed pipe has a curved 'right angle' and then goes downwards through the floor and presumably to the shower room below.

Thanks for your suggestion about turning on the shower mixer to hot and then letting it flow for a while. I did this - before the hot water came back on again, so the water was lukewarm only - and the flow was very low pressure - ie more than just a trickle but far lower pressure compared to normal. I don't think this has worked. I can however hear unusual noises in the pipes when I turn the hot water shower on and off, again making me believe this is an air bubble blockage.

Sorry I can't do photos but the shower mixer is a silver coloured Aqualisa one where there's a red button you press in, whilst moving a sort of pointy pyramid shaped 'spike' to hotter or colder, to change the water temperature. It's a bit like this one:

@PigletJohn I also took a look for any sediment or grit, as you recommended but can't see anything like that.

I can't get in touch with the plumber who originally installed the shower as I only have the contact details for the builder who uses him and the builder is currently unreachable.

The shower mixer is a very good one and unlikely to be faulty.

I think running the hot and getting the gurgling will shift the bubble.

Your valve probably has a red-painted wheel-shaped handle (not a T) and is a gate valve. With age these can seize but yours should be OK. You can give yours a quarter turn left and right to keep it free. When opening it, wind it until it starts to bind, then a quarter turn shut. This will reduce the risk of seizing. If the knob rotates freely with no effect, it is broken, but this should not have happened with quite a new valve. Never turn it hard against the stop in either direction.

P.s. the red button is a safety stop to prevent you setting the water very hot and perhaps scalding, the button enables you to turn to very hot.

Use this trick, two taps mixer, open the hot water one, then block with your palm the tap nozzle then open the cold one,keep it for few seconds.
The pressure from cold tap will travel in the hot system removing the air bubbles.
Literally you hear the bubbles travelling to the loft tank🙂

That only works if the cold is at high (watermains) pressure and can force its way up a hot pipe that is at low (loft tank) pressure.

Which is not normal (or correct) on a shower mixer