water in shower keeps going hot and cold

happy35

I have a 9 year old Vokera combi boiler that is regularly serviced by British Gas and is covered by a service plan

I had an engineer out last week as the pressure dropped he sorted this out and everything seemed fine

I had a shower last night and the water was alternating between really hot and freezing cold, the heating etc is fine and I haven't noticed this problem with the kitchen tap

The boiler failed to ignite once last night when the heating kicked in and the alarm sounded, i turned it off and straight back on and it is working fine now

Does anyone know why this would happen?

thanks

lucylucky

Is the pressure in the boiler still okay?

My mother had a Vokera and it would lose pressure regularly.

happy35

it seems ok but will check it again thsi morning and put a reply back on the forum, thanks

petebates26

What kind of shower is it Happy?

missm29

we had this with our electric shower, i was told to change the shower head and the flexible piping because it was probably full of limescale. You can get them cheap in wilkinson, suppose you could also try cleaning it.

happy35

The shower is a Miras? shower that runs off the boiler

I have checked the pressure and it is above the red line so it is in the ok range

petebates26

I don't mean to be patronising, but are you certain it runs off the boiler? A lot of Mira showers are electric.

pinkteapot

petebates26 wrote: »

I don't mean to be patronising, but are you certain it runs off the boiler? A lot of Mira showers are electric.

Following up Pete's point, if it is an electric shower, one of ours ran hot and cold and had poor flow when it was first installed. We thought it was a defective unit, but our plumber opened it up and there was a lump of something (who knows what) half blocking one of the pipes. I didn't understand why this made the temperature fluctuate but once he pulled it out the shower worked perfectly. Just wondering - if it is electric, if it might be blocked up somewhere.

Even if not, a previous poster suggested changing the head and hose in case they're blocked with limescale. If gunk inside a shower can make it run hot and cold, maybe a blocked hose can as well.

whowants2brich

Is it a fair assumption that the following are true?

a) any shower which has a brand name on it, no matter what it is, is electric? If it is plumbed into the hot water then it would just be a shower head hanging off the hot and cold water pipes.

b) any electric shower heats the water through the element, as the water passes over them then it gets hot. if there isn't enough water pressure, or too much, the water won't go through at the right speed and consequently the temperature will fluctuate. I wonder if you have something water-thirsty, like a dishwasher or washing machine running, and that this reduces the water pressure sufficiently to affect the temperature and flow speed of the shower. (when the white goods draw water, pressure falls, temp falls... when the white goods are finished, pressure rises, temp rises)

Or am I way off?

pinkteapot

whowants2brich wrote: »

a) any shower which has a brand name on it, no matter what it is, is electric? If it is plumbed into the hot water then it would just be a shower head hanging off the hot and cold water pipes.

Not necessarily. Both electric showers and power showers consist of a box on the wall with the brand name on. Electric showers are cold fill only from the mains. Power showers feed from the hot and cold water supply.

petebates26

That's what i was getting at, asking if it was an electric shower.

As whowants2brich points out, when you turn up the heat on an electric shower, it doesn't actually turn up the heat - it reduces the water flow, so that the water is passing over the element more slowly, being heated to a higher temperature.

If it's a Mira shower, it should be pretty easy to find a manual online - which should tell you how to clean the filters, which may be affecting the water flow.

If that doesn't make a difference, it may well be the heat cut out switch that's gone. If the overheat light's coming on and off as the water runs hot and cold, it could be that the cut off switch needs replacing. It's a fairly easy job if you're confident with a screwdriver (about a 17 quid part i think) - and probably still cheaper than a new shower if you'd rather call someone out.