Issue with water system

LeoN88 · 26 Aug 2010 at 16:50

So for any of you out there which may have some experience or be in the trade i have an issue with the workings of the hot water flow through the house. I have had a plumber come down to look at the issue and as yet cannot seem to solve it and will be asking another friend of his who has more experience to give advice...

The problem is that the cold water is over riding the hot for example:

The water in the bath runs hot yet the shower head will only run hot when the bath is running otherwise it comes out cold.

In the down stairs showerroom however the water from the shower will not run hot no matter what other water device is turned on yet when the shower is running the tap in this room and the kitchen will turn hot.

There is no problem with the boiler as it is only 5 years old (megaflow) and nothing wrong with the cylinder as the plumber checked it.

if anyone could help would be greatly appreciated

Thanks leon

Dave M · 26 Aug 2010 at 17:43

The flow from the showers isn't enough to trigger the combo to turn the boiler on?

Oh you mention cylinder - is the hot water fed from a tank then? Where is this and where is your cold tank in relation to the shower heads?

TheCrow · 26 Aug 2010 at 17:48

We had similar and it was a valve on the boiler that lets the cold into the hot water flow. Dont know if it was a mixer valve or not but think it got sticky so sometimes it would be fine others it would be cold.

LeoN88 · 27 Aug 2010 at 12:18

Telescopi said:
The flow from the showers isn't enough to trigger the combo to turn the boiler on?

Oh you mention cylinder - is the hot water fed from a tank then? Where is this and where is your cold tank in relation to the shower heads?

The hot water is fed from a tank which is located on the ground floor. We don't have a cold water tank in the house? i'm assuming it just comes directly from outside to in. (new house 5 years old)

rossyl · 27 Aug 2010 at 13:37

Megaflow is an unvented high pressure cylinder. I believe this provides all your hot water. Your cold water I think will be mains. There is no combi.

Seems an odd problem, and what you really need is a person who is knowledgable about the type of system you have. Rather than getting a person more accustomed to combi's.

If I were you I'd try a thread on the DIYnot forums.

Participant · 27 Aug 2010 at 13:37

It sounds like your cold mains water pressure has not been correctly regulated...cold will normally be at a much higher pressure than that supplied by the hot from the unvented cylinder.

Get your plumber to check that the correct pressure regulating valve is fitted before the shower mixers etc, or that it's operational. It could be a stuck PRV valve.

Archy · 27 Aug 2010 at 14:03

If your cylinder is indeed a Megaflo (manufactured by heatrae sadia) these cylinders have a PRV and cold water combination valve with them (for balancing the cold water going to showers etc) which can often malfunction. Perhaps get your plumber to check these out and see if they are faulty. Could be the source of said problem.

Readily avaibale from any plumbers merchants that deals with interpart (baxi spares) and something we sell ourselves reguarly!

Duke_ · 27 Aug 2010 at 15:03

I think Robbie / Archy might be onto something

I assume the showers are both equipped with Thermostatic mixing valves - ie they are one tap to turn on and a lever / tap to change the temperature - not two separate taps?

I was going to suggest turning down your incoming cold mains at the stopcock to reduce the pressure but if it's a pressurized system them you'll just reduce the hot water pressure too...

'In the down stairs showerroom however the water from the shower will not run hot no matter what other water device is turned on yet when the shower is running the tap in this room and the kitchen will turn hot.'

I don't quite understand what you mean by the above sentence - please could you explain it? Are you saying the taps in the kitchen and that room don't get hot unless the shower is running?

When did the problem start? Were there any changes made to your existing HW system?

LeoN88 · 27 Aug 2010 at 15:47

Alex_S said:
I don't quite understand what you mean by the above sentence - please could you explain it? Are you saying the taps in the kitchen and that room don't get hot unless the shower is running?

Thats exactly it.

Alex_S said:
When did the problem start? Were there any changes made to your existing HW system?

Well in the past few months for instance, the hot water from the downstairs shower room tap has only dribbling out.

At that time as well when the heating was switched off there was the same problem as what we have now. But when it was turned on there was no problem with the hot water..

However now it doesnt make any difference if switched on or off (heating) its basically got worse over time and now no hot water unless certain taps/baths/showers etc turned on.. very puzzling..

Thanks for the comments so far from you all by the way will be looking into it now!

Archy · 27 Aug 2010 at 15:52

If it had just been showers that were the problem I'd have been suggesting thermostatic mixing valve on the showers at fault, but when its taps as well and a megaflo, I'd be looking at the PRV/CW combi valve. Hope you get sorted out!

St0rmer66 · 27 Aug 2010 at 17:42

First thing I'd look at is, as others have said, is the pressure reducing/regulating valve. Chances are it will also be controlling the cold (to get a 'balanced supply') so if it's faulty it will affect all sorts.

LeoN88 · 5 Sep 2010 at 10:35

well i got it all sorted told the bloke what had been suggested and you were right the pressure coming in was 6 bar so got it reduced to 4 bar now everything perfect! (he assumed that the water board could have increased the pressure) so thanks ocuk!