Running out of hot water

[tr7v8]

Help please, problem suddenly started today. We have gravity hot water tank in the airing cupboard, cold water tank in loft. Power shower in the bathroom, only the hot water cylinder is fed from the cold tank everything else is run from the mains. Whilst having a shower today the power shower started to struggle for water flow then cut off completely. I switched it off & covered in soap ran a hot water tap to get some water to rinse the soap off & found no flow! Opened the loft hatch & the cw ballcock was open with water running into the tank. A few minutes later we had running hot water again!
Help! Wife had a shower early AM OK, but this repeated early evening.

Edited by tr7v8 on Monday 8th February 20:42

[tr7v8]

OK thanks for the suggestions. The flow into the tank seems pretty good & the ballcock is new so unlikely to be that. I've just raised the ball so the tank starts from a higher level when the shower is on.
I think with the cold weather & the colder cold water the shower which is thermostatic is demanding more hot than before to make up the selected temp. The shower is a new one so the flow rate could be different.

[tr7v8]

Welshbeef said:

Might you be doing a Lester Burnham while in the shower .

I had to google that, nope don't take me that long!

[tr7v8]

No changes to shower head & no long showers. In fact no changes to anything obvious. Today I've raised the cold water tank level by 35mm & also this time put the plug in the bath. Rough measurements give around 40litres before it starts sucking air.
Tonight's plan is to watch the cold water tank whilst the Missus showers & see what is going on. There is some sheet like material in the CW tank which I assume is limescale. I'm wondering if that could block the outlet?

[tr7v8]

OK few more tests tonight. Whilst the wife had a shower I checked the cold water tank. It barely drops 15mm during the whole cycle & the shower starts to surge at around 3 mins. I put the plug in today whilst having a shower & I reckon around 40 litres is all you get before it stops. Never had an airlock before but Driverrob maybe onto something. I tried balling a rag over the mixer tap but only succeeded into soaking the kitchen & me!

[tr7v8]

Welshbeef said:

Do you live in a hard water area?

Is it a mixer shower /power shower?

If yes and it's not brand new and you don't have a water softener then its furred up and only option is to replace the power shower (in Reading it's very hard water so you burn through shower heads probably 4 a year so no point in buying pricy items, dishwasher uses loads of salt, and the mixer shower I've personally replaced a few times seem to last anywhere between 2-3 years use dependant I guess.

Yes it's a very hard water area but the shower is less than 6 months old, it is a replacement mira same as the other one which died after 18+ years.

[tr7v8]

Salesy said:

it sounds like a blockage to me. might be worth checking all hot taps in property to see if it tails off at around 40 litres from various locations.

If it happens to all then probably a blockage

Got a horrible feeling you could be right! It is looking like this or an airlock!

[tr7v8]

Welshbeef said:

tr7v8 said:

Yes it's a very hard water area but the shower is less than 6 months old, it is a replacement mira same as the other one which died after 18+ years.

When shower is cold try all other hot taps in the house - could be one pipe is more furred up than the others.


Also don't discount the fact the Shower could have failed very early - but if cold from all other taps then it's not that.




How long is your hot water on every day? For a family of 4 we have it running from 5am to 7:30am and then 4pm to 7pm every day (don't wash up anything as we use dish washer so hot water is purely for bath/shower. )

The hot water is on continuously. The shower doesn't run cold, it surges & stops because it can't get enough I assume hot water. But when this happens I get no hot water in each of the bathroom taps either. Give it a few minutes & flow is back on all of them.
I have just run the hot water tap in the kitchen for 20 minutes or so & had no issues, this is the end of the hot water feed from the tank. Stayed hot all the time as well & from rough measurement I reckon this is 60ish litres.
Just to clarify the shower is fed direct from the hot water tank (Essex flange!) & another pipe on that T goes bath tap-basin tap then down to washing machine then kitchen tap then downstairs loom which is the end.

[tr7v8]

Welshbeef said:

tr7v8 said:

Yes it's a very hard water area but the shower is less than 6 months old, it is a replacement mira same as the other one which died after 18+ years.

When shower is cold try all other hot taps in the house - could be one pipe is more furred up than the others.


Also don't discount the fact the Shower could have failed very early - but if cold from all other taps then it's not that.




How long is your hot water on every day? For a family of 4 we have it running from 5am to 7:30am and then 4pm to 7pm every day (don't wash up anything as we use dish washer so hot water is purely for bath/shower. )

The hot water is on continuously. The shower doesn't run cold, it surges & stops because it can't get enough I assume hot water. But when this happens I get no hot water in each of the bathroom taps either. Give it a few minutes & flow is back on all of them.
I have just run the hot water tap in the kitchen for 20 minutes or so & had no issues, this is the end of the hot water feed from the tank. Stayed hot all the time as well & from rough measurement I reckon this is 60ish litres.
Just to clarify the shower is fed direct from the hot water tank (Essex flange!) & another pipe on that T goes bath tap-basin tap then down to washing machine then kitchen tap then downstairs loom which is the end.

[tr7v8]

Welshbeef said:

tr7v8 said:

The hot water is on continuously. The shower doesn't run cold, it surges & stops because it can't get enough I assume hot water. But when this happens I get no hot water in each of the bathroom taps either. Give it a few minutes & flow is back on all of them.
I have just run the hot water tap in the kitchen for 20 minutes or so & had no issues, this is the end of the hot water feed from the tank. Stayed hot all the time as well & from rough measurement I reckon this is 60ish litres.
Just to clarify the shower is fed direct from the hot water tank (Essex flange!) & another pipe on that T goes bath tap-basin tap then down to washing machine then kitchen tap then downstairs loom which is the end.

Ok then try this:-
1. Take shower head off and run it - there might be a tiny blockage in the head
2. Take the chrome flex off is that blocked in some way or another?
3. If 1&2 don't do anything take the shower off the wall and turn the water back on this will isolate if it's the shower or between shower and hot water tank.

OK but this wouldn't cover the hot water flow in the bathroom stopping at the same time.

[tr7v8]

Welshbeef said:

tr7v8 said:

OK but this wouldn't cover the hot water flow in the bathroom stopping at the same time.

Let's get the shower fixed first.


Also why is the hot water on heating it up all day long? Utter waste of £ on gas to heat it up. You simply do not need to do that.

But the two things are linked, eg no shower means no hot water in the bathroom, both feeds are from the hw tank. A bit of googling has hinted that the issue maybe limescale build up in the tank outlet. But why would that halt the flow after 3 minutes or 40 litres!
The tank is very well insulated & rarely fires the boiler. I tried both & it made no difference to the gas bill. The house is also occupied all day & night.

[tr7v8]

bomma220 said:

Could you post the model number of the Mira shower please? Also where is the HW cylinder in relation to the shower,

eg ground floor / 1st floor, house or bungalow?

OK Shower is a Mira Event XS Thermostatic & it is above the bath, same floor (upstairs) as the HW tank.
Cold water tanks is immediately above.

[tr7v8]

Welshbeef said:

herewego said:

Did you say there was sheets of limescale in the cold tank? Is there something to put in the cold tank to dissolve the limescale?

Edited by herewego on Wednesday 10th February 10:09

It could be a chunk of that has dislodged and somehow found its way to causing issues in the bathroom.



Probably worth changing the header tank - cheap as chips anyway and yours no doubt is 18++ years old and scaled up.
The hot water cylinder could also be really scaled up which may mean replacement.

I have pretty much come to that conclusion. I ran the bath today as a test & was getting 1 Litre every 19 or so seconds which is pretty slow. The bath filled up eventually but the shower obviously has a greater demand from the hw tank.
Googled low pressure HW & there was a guy on Youtube saying that the neck of the HW tank fouls up with scale.

[tr7v8]

Bomma220 thanks for the comments but it isn't the filter. If the filter was blocked you get cold water out of the shower, the previous even had that. Also any vacuum would be pump to filter all of 20 or so mm.
The plan today was to buy some Fernox descaller & descale the HW circuit. worth a try for £60 anyway.

But now completely confused just had a shower & all is back to normal, full water flow on bathroom taps (1litre in 3 secs or so) & the taps work once you've had a leisurely shower & turned the shower off.
So Fernox purchase on-hold at the moment!

[tr7v8]

Latest update!
Yes we are back where we were before, shower runs for around 3 mins tops before it starts to surge & splutters to a halt with the pump screaming. At this point there is no flow to any of the HW taps in the house. It will eventually come back after quite a few minutes.
Flow from all hot taps is poor, starts OK but within a few seconds seriously diminishes to a trickle.
Tried linking hot & cold taps together today, made no difference. Convinced it must be lime scale in cold feed to hw water tank or at top of tank.
Have just ordered 6kg of Fernox DS3 & have an appointment with draining it all down & flushing with the DS3 mix.

[tr7v8]

g7jtk said:

Does the hot water cylinder have either a Surrey or Essex flange fitter to the outlet?

Yes it does, I think.

[tr7v8]

OK guys finally fixed it. 6Kg of Fernox DS3 descaler, put into the drained cold water header tank & drew it down through the hot taps. Then left for 6 hours with the boiler running. After around 4 hours of doing 15 minute drains of a pint or so the taps started running at full flow. I also cleaned probably a couple of kilos of scale from the header tank, manually using a dustpan & bucket. Ha to clean all the filters after, both shower & mixer taps but it all works, best hot water flow for years. Thanks for the suggestions guys, got there in the end.