Showers & Non-return valves

Zxcvbnm

Some time ago we paid for a (v v expensive) callout from the manufacturer of our boiler because our boiler was under-performing and no plumber had given a satisfactory explanation of why.
Anyway the engineer that came out diagnosed the shower as the culprit, explaining that it had not been fitted with non-return valves. If we turn the shower up to it's maximum temperature setting we can get decent hot water in the rest of the house.

Is my understanding correct that because there is no non-return valve on the shower hot feed, cold water is coming through the shower and "contaminating" the hot water?

The hot feed is quite easy to access beneath the bath. If I were to cut the pipe after it splits for the bath tap and fit something like a compression-fitted non-return valve or similar, should this remedy my problem? This valve would be about a meter and a half from the actual shower but that's the closest I can get without chiseling out the tiles!

Is there a simpler (LOW COST!!) solution?

David

rrf494g

some more information would help me. The shower controls the temperature of whole hot water system? What does the boiler supply? Hot water plus central heating? The shower controls the temp even when it is not flowing itself? What type of boiler is it? a combination boiler has no header tank, and no hot water storage tank -it heats water as you use it. A "conventional" boiler has both (and may in addition have an immersion heater fitted in the hot water tank).

Sounds like there may be more than an a non-return valve missing.
regards

Zxcvbnm

Ok, I know it sounds odd -

Just to boil it down.

- There's a combi-boiler supplying hot water and central heating.
- There's a thermostatic mixer shower (standard horizontal bar type) in the bathroom.
- If the thermostat on the shower is low - the supply of hot water (e.g. to the kitchen or bathroom basin) is poor.
- If the thermostat on the shower is max - the supply is OK.

When the expensive engineer came out, he pointed out the the shower head was drizzling when we ran the basin and then he set the thermostat to maximum and lo and behold - we had hot water. He suggested that it was possibly a) a faulty shower AND b) had not been fitted with NR valves.

Now I actually fitted a new shower and this appeared to solve the problem for a while*. But I was nervous about cutting pipes and stuff like that to fit valves or whatever. I'm a little more confident on BASIC plumbing jobs now.

I've spent some time trying to make sense of why this would affect the hot water and my "contaminating" statement above is the best I can do!

* I'm not 100% on this - which is why I didn't mention it initially - it may just be that we got in the habit of leaving the thermostat high on the shower.

Is that any better

keystone

EDIT - Just read your reply which you were typing as I was typing this so you can largely IGNORE this post but I'll leave it in place for the benefit of others who may have the situation I'm describing.

It sounds as though your shower is incorrectly piped.

It is clearly not an electric shower as that only has a single cold supply at mains pressure.

If you have a combi boiler and no HW cylinder or cold water storage tank (CWST) in the roofspace then both your hot and cold supplies to the shower will be at mains pressure and therefore balanced and neither will overwhelm the other unless the shower is passing and you have crossover.

If you have a system arranged with a HW storage cylinder then that is where the hot supply is taken from. Is that the case? If so is it vented with cold water storage in the roof or unvented? Lets deal with the vented scenario specifically but it would be useful to know which type you have:

If it is vented then the supplies for the shower (both hot and cold) should be independent from other drawoffs the cold coming direct from the CWST and the hot from the HW cylinder either via a suitable flange or teed off the vent and you will a balanced supplies at iro 0.25 bar.

If, however, your hot for the shower is derived from the HW cylinder fed by the CWST BUT your cold for the shower has been taken from the mains riser feeding the CWST then the cold will be at iro 3 bar and the hot at iro 0.25 bar so the cold will always overwhelm the hot if they come into contact and if the shower is passing then yes the cold will contaminate the hot supply.

The solution to this is NOT to fit a non-return valve (which would be a bodge) but to pipe it correctly. Hope that helps but to be absolutely definitive agree with previous poster and fuller details are required.

Cheers

ormus

its more likely to be the shower mixer at fault. i doubt fitting NRVs will cure it.
ive got NRVs fitted, as advised by a plumber. another plumber told me i didnt need them on my system.

afaik you only really need them to stop, back syphoning. ie if the shower head falls into the bath water.

Zxcvbnm

ormus wrote: »

afaik you only really need them to stop, back syphoning. ie if the shower head falls into the bath water.

This is what all my googling seemed to imply - noone seems to mention requiring them for the feed.

keystone

Zxcvbnm wrote: »

- There's a combi-boiler supplying hot water and central heating.

Thank you. The comments in my previous post concerning a more conventional setup are not applicable in your case.

- There's a thermostatic mixer shower (standard horizontal bar type) in the bathroom.
- If the thermostat on the shower is low - the supply of hot water (e.g. to the kitchen or bathroom basin) is poor.
- If the thermostat on the shower is max - the supply is OK.

Is the thermo mixer of the "pressure balanced mixer shower" type? It should be of this type for use with a combi. You may possibly have fitted the wrong type of shower valve and it does sound as though you are getting crossover. What shower valve (make/model etc) is it that you have fitted?

Cheers

Zxcvbnm

keystone wrote: »

Is the thermo mixer of the "pressure balanced mixer shower" type? It should be of this type for use with a combi. You may possibly have fitted the wrong type of shower valve and it does sound as though you are getting crossover. What shower valve (make/model etc) is it that you have fitted?

Cheers

I'm in the office so I can't check - but it's definately a gainsborough one - bought in B&Q I think - and of the models on their website it most resembles the GS300.

EDIT : According to their website this type should be ok with a combi boiler.

keystone

Sorry - got distracted. Yes I agree the GS300 is suitable for use with a combi. What is the make /type of the combi? Fluctuating water temp is a symptom of the boiler not modulating properly.

Following on from your previous description if you leave the shower set (say) to a mid position temp and run the bath tap do you get fluctuating temperature at the bath or does it just produce tepid water?

Cheers

PS I have to go out to a job in about ten minutes so we may have to continue this later unless someone else comes along to help you in the meantime.

Zxcvbnm

Can't remember the make and model. It's a fairly standard non-condensing one.

If the mixer is set low or mid-way temperature doesn't generally fluctuate - it just doesn't get very hot.

From what I'm hearing - it sounds like ANOTHER broken shower valve - as these appliances shouldn't allow crossflow - but this one is just approaching it's second birthday - it's predecessor was around 3 years old. Is that normal? Two valves in 5 years? Am I just unlucky?

(And is there no chance a £2 non return valve would fix(/bodge) this? )

ormus

i would change it for a mira one. you can get spares for mira mixers, inc the seal kits.