Waterfall shower with poor hot water pressure - boiler problem?

[Irene27]

I have a waterfall shower. The water pressure used to be very good but is now weak when the shower is running hot.

The bath taps also run hot then cold, hot then cold again. It's not possible to run a hot bath.

I have a Potterton Titanium boiler. I called out a boiler guy but he claims it's working beautifully and there are no problems. He had me run the tap and said that because the boiler was firing, that meant there were no issues.

He charged me £30 for this golden advice, then when I told him to wait in his van while I went to the cash point to get his money, he drove away!

A quick google suggested problems with scaling inside the heat exchange can cause this issue. However I'm in a soft water area and the boiler has been treated with fernox? Any advice before I try a second boiler engineer?

I hate it when workmen run away. It always suggests the problem is intractable and an easier £80 can be found elsewhere. Not good juju.

I had something like this happen. Shower was too cold, bath was running cold. Had holier guy out a few times. It actually was a faulty mixer in the shower so the cold water was running into the hot supply. It was affecting the bath too. Hot water at boiler was fine but water elsewhere upstairs was too cold.

Sorry, meant boiler guy. Replaced shower mixer and water problem was solved.

Hopefully PigletJohn will be along to solve the problem for you.

I wondered about the mixer tap but I've tested it and the water pressure in the shower is ok when run cold. It drops off as the temperature increases.

I've also tried turning the central heating off to see if the boiler is underpowered, but no improvement.

Just had this with my shower. Took the cartridge out and soaked it in descaler for an hour which solved the problem. If hot water is coming out of other taps fine then sounds like the boiler isnt the problem.

I might be talking nonsense here but in our case the cold water was crossing over under pressure and pushing back the hot water so the water pressure decreased when the water should have been getting hotter. Do you have a mixer on your bath too?

Ah, I understand MsForestier. Yes, we have a mixer on the bath. I'll try a plumber next and ask about this.

Thank you!!

Hope it solves for you. I had Scottish Gas out three times and I said to the last one 'could it be the cold water crossing over?'. He phoned his supervisor who said it might be so try a plumber. We had three mixers in the house but it was the shower mixer. Ruddy frustrating it was. I had floorboards up looking at valves and was on the net researching it until I found someone with a similar problem.

Does the fluctuation in temp happen on all outlets or just the shower/bath. It's a process of elimination, if the hot water is consistent in the kitchen sink and basin then that would indicate it's not boiler related.
Although if it is boiler related it may well be the heat exchange plate.

In our case the kitchen mixer was fine but the cold water was crossing over upstairs at the shower and this also affected the bath water temp.

I live in an all electric house so know nothing about boilers, but when my sister moved into her house she had problems with the bath water running hot and cold.
When the boiler was serviced she mentioned the problem to the engineer and he told her that although the boiler was fine it wasn’t big enough to cope with the demand placed upon it when the bath was run and that when the time came to replace it she should get a bigger one. He also suggested that she should run the bath water very slowly - this has helped regulate the temperature of the water coming out of the tap but it requires the patience of a saint and the bath water is never what you’d call hot.

Is it a combi boiler, and is the water colder in winter than in summer when you draw a lot of it (e.g. when filling a bath or using a drencher shower)?

That's what combis do.

Fill a bucket under the shower when it is tuned to hot; time it, calculate how many litres per minute it delivers, take the temperature of the water please.

Then do the same at the basin tap.

I am expecting to find that the higher flow leads to a lower temperature.

Then please take the temperature of the incoming mains water at the kitchen cold tap.

If you have a cylinder, not a boiler, it will be something different.

If you have a cylinder, not a combi boiler, it will be something different,

I meant.