Lukewarm shower/bath, poor hot water flow

[Christop]

Hi, I have had an ongoing issue with a shower/bath mixer that appears to be getting worse.

The system runs of a combi boiler.

The temperatures of the bath/shower water is lukewarm at best, measured earlier as around 32 deg max and this fluctuates. The thermostatic cartridge was recently replaced due to being clogged with scale (very hard water area - the whole water system was only installed ~2 years earlier) and is configured to max heat.

The shower is concealed but I have removed the front plate and exposed the outlets. Flow rate of cold water coming out is much higher that warm (I would guess about 3-4 times as much).

I don't have an issue with other taps in the house - hot water is too hot to touch but clearly the flow rate is much lower.

I am wondering what the likely cause is with my limited plumbing experience. As stated the cartridge was recently replaced and there is a big imbalance in the flows, but shouldn't the cartridge "balance" the amount it takes in?

Is it normal for the hot water flow to be that much lower than cold water flow? Would the issue be caused by a possible blockage in the boiler (considering the hardness of the water) or could the supply pipes be blocked?

Grateful for any advice.

 

[rocketmanbkk]

Your cold flow is probably mains pressure & your hot is from combi so that'll be normal that the flows different

With the shower front off can you open the hot & see how hot it gets?

Maybe the cold mains is pushing hot, maybe not

 

[steadyon]

With a combi I'd expect the pressure of hot and cold to be virtually equal. Given that other hot taps seem to be OK, this suggests there is a restriction of some sort in the hot feed to the shower. Many showers have non-return valves and filters in both hot and cold inlets. The hot side particularly is prone to blocking with lime scale in hard water areas.

My first port of call would be any non-return valves and filters integral to the shower. See if you can get at these, remove, soak in de-scaler (such as Kilrock, white vinegar) and see if it makes a difference.

 

[Christop]

Thanks for the responses.

The temperature on the hot side is upwards of 48 deg, although its hard to measure because some cold water comes through.

Both non-return valves and filters have been removed, cleaned and replaced. There was a huge amount of scale behind the hot side but I have cleaned out the bits I can see. At first this improved things (bath still never got that hot) but it has since got worse.

I have a video of the shower outlets that I will try to post later for more info.

 

[Christop]

Here is the video showing the outlets:

[video=youtube;lO9DCIA4gdc]https://www.youtube.com/watch?v=lO9DCIA4gdc[/video]

 

[Frog67]

A Ongoing issue?
B has the shower ever worked correctly?
If yes to A and no to B then the valve itself may not be compatible with a Combi boiler.
Check the installation instructions if you still have them or look for the model make on the valve itself.
You may find that if the above is correct you may only have to replace the cartridge with the correct type.

 

[Christop]

A Ongoing issue?
B has the shower ever worked correctly?
If yes to A and no to B then the valve itself may not be compatible with a Combi boiler.
Check the installation instructions if you still have them or look for the model make on the valve itself.
You may find that if the above is correct you may only have to replace the cartridge with the correct type.

Sorry, can you clarify? Do you mean the non-return valves? If so they are parts with the shower unit itself (manufactured by Grohe). Why would they not be compatible with the boiler? How would a different cartridge help?

 

[Radioman]

If the shower valve worked OK after the new system was installed but doesn't work now after the new cartridge then the wrong cartridge has been fitted. If it never worked correctly after the new system was fitted then it is the wrong valve period.
Ps get a water softener and save agro and money

 

[Frog67]

If the shower valve worked OK after the new system was installed but doesn't work now after the new cartridge then the wrong cartridge has been fitted. If it never worked correctly after the new system was fitted then it is the wrong valve period.
Ps get a water softener and save agro and money

Sorry for the confusion but Radioman's explanation is what i was trying to say.

 

[Radioman]

Yes but which fault is it, OK before cart change and not now or never been any good???

 

[Christop]

The shower and boiler have been in place since purchasing the property.

The shower and bath unit is the rapido t universal thermostatic mixer for concealed installation by Grohe (the forum wont let me post a link). I am not aware of anyway to change to a different type of valve or cartridge.

The water in the bath has never been particularly hot (it is fine on other taps) but has gotten noticeably cooler since installing a water conditioner on the pipe into the boiler (was no space to put it above the stop tap.

 

[Radioman]

A quick look at the tech spec of that valve https://cdn.cloud.grohe.com/tpi/1000/1800/1890/1895/1895245/original/1895245.pdf
says that it is not suitable for systems with major pressure differences between hot and cold supply. Also states that inlet hot should be in the range of 60 to 70 C, max inlet 70C, hot inlet is the left cold to the right.
Don't think you will ever get this working, most of these offshore valves work best on unvented high pressure systems.

 

[Plumbstar Tom]

I just think you need to reduce the flow rate of the cold inlet.

 

[Radioman]

I just think you need to reduce the flow rate of the cold inlet.

That's been discussed many times on here and it's not a solution, flow rate and pressure etc etc.

 

[Plumbstar Tom]

honestly I have been to plenty of installations where flow limiters are supplied with the shower and not fitted. I have fitted them and it fixed it. see page 17 of this (different shower I know) http://www.hansgrohe.de/medias/sys_master/celum_assets/16__hrgh0242_pdf.pdf?1

I am not speaking about cracking down the isolator slightly or anything like that

 

[Christop]

Ok but rather than reducing the flow of the cold water, how do I increase the flow of the hot water? I have been 3-4 bar of pressure going into the house, so why is the flow of the hot and cold at the shower/bath so different? Is this just a natural result of the pipes and the boiler? Or is there a blockage somewhere?

 

[Radioman]

Depends on how the conversion to a combined was done and it's also a function of the combi to reduce the flow and pressure of the hot. Try it and see what happens, you can reduce the flow rate of the cold but not the static pressure. This is why some valves are ported for combi and some for gravity etc.

 

[Plumbstar Tom]

afraid you cannot really improve the hot flow without the expense of moving to a fully unvented systems which will be a 4 figure sum I'm guessing. Its the way combis work, slow the flow to heat it up. You could have 10bar going into the house an it wouldn't help

 

[Christop]

Understood, but the instructions from the boiler (Ideal iMini 30kw - again can't post the link) say that the boiler can put out 12.4 l/min. At the moment its closer to 3 l/min based on what the bath puts out at hottest setting.