Combi boiler + hot water flow regulator

[nero44]

Hello,

I have a Vaillant Ecotec plus combiboiler, which is powering hot water supply and central heating. We recently had two bathrooms refurbished, but they were done sequentially. I am seeing some occasional hot water issues only in the second bathroom. I believe this could be due to a missing flow regulator in the second bathroom, as both of them feed off the same single hot water supply line and both use shower mixers form the same manufacturer. I can also see that the pressure/flow on the first one is weaker, but much smoother.

My questions is, is this expected behaviour? I.e. when I open the hot water full throttle, hot water comes out at first, but then it seems like the boiler cannot supply as much as quickly and autoregulates the temperature down? On the boiler I see the temp drop to just above 40 degrees. When I switch off the shower and then just open any tap in the house, the boiler then runs hot normally to +60degrees. The shower then also seems to work fine, provided it is not opened full throttle. All of this happens when central heating is off and no other major hot water feeds were required at the time. Looking at the visible pipework, I can definitely see a flow regulator installed in the first bathroom just above the shower head. This bathroom works 100% fine. Is this something I need to take up with the installer, or could it simply be a missing flow regulator in the second bathroom? Is this common?

Greatly appreciated for any views on this pls.

 

[Johntheo5]

The DHW temperature the boiler can supply (even if set to 60C) is dependent on the flow rate and the (mains) cold water temperature, my mains temperature is 10.5C just now, so a 30kw combi will supply 8.7LPM at 60C or 14.6LPM at 40C., a 32kw, will supply 9.3 & 15.6LPM and a 35kw, will supply 10.2 & 17.0LPM and so on. You should install a restrictor in the second shower to give the same flow when both are running together. What is the power output of your boiler, the exact expected flowrates can be easily calculated then.

 

[nero44]

The DHW temperature the boiler can supply (even if set to 60C) is dependent on the flow rate and the (mains) cold water temperature, my mains temperature is 10.5C just now, so a 30kw combi will supply 8.7LPM at 60C or 14.6LPM at 40C., a 32kw, will supply 9.3 & 15.6LPM and a 35kw, will supply 10.2 & 17.0LPM and so on. You should install a restrictor in the second shower to give the same flow when both are running together. What is the power output of your boiler, the exact expected flowrates can be easily calculated then.

Thanks, I will check the power output and post back. Not on location at the moment.

But the thing is, I haven't even checked what happens when both showers are running at the same time. I get this issue, when only running the second shower alone. The bathroom before refurb also had a strong flow restrictor, so we never had any issues there. It is only since we refurbed the bathroom with an overhead rainfall (although small 20cm) showerhead. n.b. the other bathroom also has a 20cm rainfall showerhead but with restrictor and works fine.

I guess I need to unscrew the 2nd bathroom showerhead and confirm. My boiler was serviced mid December, so I don't think the unit itself is the issue.

 

[Johntheo5]

Just run each shower separately into a bucket for exactly 30 secs and measure this with a 1 litre container, X 2, this will give the flow rate in LPM, note the boiler output and post back.

 

[nero44]

Just run each shower separately into a bucket for exactly 30 secs and measure this with a 1 litre container, X 2, this will give the flow rate in LPM, note the boiler output and post back.

So my boiler is Ecotec plus 831, older 2005-2011 range, it appears to output 24.4 kw.

I've also measured the LPM:
First bathroom with flow regulator: 5.76 LPM
Second bathroom w/out flow regulator: 9.44LPM

So quite a lot more than the first one. What concerns me now, is that we never even run the showers at the same time, just the second one alone occasionally leads to temperature drops. Any advice would be greatly appreciated.

 

[Johntheo5]

The 831 MIs show a output of 24.4kw to CH and 30.8kw to DHW, so,
Assuming mains temp of 10.5C (few days ago), shower1 at 5.76LPM only requires, 5.76*60*(40-10.5)/860, 11.85kw at 40C or 5.76*60*(60-10.5)/860, 19.89kw at 60C
Shower2 at 9.44LPM requires 9.44*60*(40-10.5)/860, 19.43kw or 9.44*60*(60-10.5)/860, 32.6kw at 60C, your boiler has a max output of 30.8kw so the temperature rise at 9.44LPM is, 30.8*860/60/9.44, 46.76C giving a HW temperature of, 46.76C+10.5C, 57.26C, only 2.74C less than 60C.
You shoud have no problem whatsoever running at any temperature below 57C at 9.44LPM.
Even if you could run both showers together at a total flowrate of, 5.76+9.44, 15.2LPM, you should still get a temperature of 39.54C, (30.8*860/60/15.2))+10.5, 39.54C