valiant combi boiler

[dongiven]

just moved into house with a valiant combi boiler. It seems to work well.

plenty of hot water. central heating working perfectly.

However when I turn on the shower i am unable to control the temperature. The water is so hot that it would leave one hospitalized. I am able to have a bath!

i am fed up having to go to the gym for a workout so that i can have a shower. help!!!!!

 

[Bahco]

Sounds like a shower problem. Is it only the shower water that is scalding all other hot supplies are fine?
If so your thermostat is kaput and needs replacing.
Not worth changing if your shower is electric, more cost effective to buy a new shower.
If all hot water is scalding turn down your hot water thermostat on the boiler.

 

[dongiven]

The shower works through a mixer tap. Hot water coming from the combi boiler one side cold water the other. Unable to cool the hot water sufficiently to have a shower. Cold water coming from the header tank ...pressure quite good.
There is a thermostadt to control the temperature of the hot water through the central heating but none to control the temperature of the instant hot water.
Does anyone know if the temperature of the water from the valiant combi boiler can be regulated? if so how?

 

[kevplumb]

your cold is tank fed you have unequal pressure so a diverter shower will be to sensitive
what model of vaillant is it?

 

[Bahco]

Kevplumb is right (beat me to it)
You need to feed the cold side of the shower from the mains supply.
Easiest way is to blank off your existing cold supply to the shower from the cistern in loft and divert existing pipe to the pipe that is feeding your cistern so balancing the pressures.
Don't forget to turn off mains and drain cistern first

 

[ChrisR]

If you have decent mains pressure you could just get the flow restrictor taken out of the combi. Then you'd get more, cooler, water. Bit of a botch but it works. If you'd only tell us what boiler it is...

You should not leave your mixer as it is - all the above are correct.

 

[msgodden]

Are you not meant to use a thermostatic mixer shower with a combi boiler system, rather than just a normal hot& cold mixer which is sensitive to pressure/temperature fluctuations?

 

[ChrisR]

That won't help one iota with unbalanced supplies like the situation here.
In fact thermostatic mixers give a lot of problems with a lot of combis even when things are plumbed properly.
I have explained a dozen times before -but basically TV decides it needs less hot so it reduces hot flow - so the water from the combi gets hotter - cycle winds up and up until the combi goes out cos the water's too hot. Shower goes cold then cycle repeats.

"Pressure balanced" showers are better, but aren't thermostatic!

Later combis are better than earlier ones. Depends on length of pipe between valve and combi too, as well as mains pressure, other users, scale in combi, resistance in pipes.......