New shower lukewarm - balancing issue?

[davidjatt]

Hi all, I have just fitted a new shower room with thermostatic shower and a basin. because our water pressure is awful I also fitted a 270lt tank with pump, so there is plenty of pressure/flow. There is already one thermostatic shower in place. See diagram for pipework.

The old shower works great with this setup, pressure is so much better than before.

The new shower never gets more than lukewarm, even with boiler set to 60 (max). I already replaced the thermostatic cartridge (see other thread haha) but still the same.

- With the shower off, the basin tap DOES get hot, then if you turn the shower on as well the shower starts hot for 30 secs but then both the shower AND basin tap go lukewarm.

- If the old shower is running, then I turn the new one on, the old one also goes lukewarm after a few seconds.

Is this some kind of balancing issue? See pic - The pipework from the tank is 22mm until it splits off to go to old shower, and new-shower-plus-boiler. All other pipework is 15mm. I took the cold feed for the new shower off from the boiler cold feed about 50 cm before the boiler as that was a handy place.

 

[cross thread]

Check to see if old shower is passing ,turn old shower on till hot then off turn new one on and feel hot into old shower to feel if it goes cold.

 

[davidjatt]

Thanks, tried that but it stays hot. So presumably that one's doing what it's supposed to.

 

[cross thread]

Checked the basin ?

 

[JohnD]

What colour is your hot water cylinder?

 

[danfre]

Hot and cold on new shower wrongly piped up ?

 

[Madrab]

Is it a combi boiler? If so what is the pressure of the mains against the pressure of the pump for the cold cistern? If they are significantly unbalanced then that can cause a problem.

The other alternative, as suggested is check that the pumped cold isn't pushing it's way past a mixer somewhere, is the basin a mixer tap and does it have ISO valves. If so isolate there and try that.

 

[dilalio]

What colour is your hot water cylinder?

Don't see any mention of a cylinder.
It's a combi.

 

[JohnD]

Don't see any mention of a cylinder.
It's a combi.

I saw a reference to "I also fitted a 270lt tank with pump, so there is plenty of pressure/flow. There is already one thermostatic shower in place. See diagram for pipework."

Which did not sound typical of a combi.

But I see now it is a cold water cistern with pump.

 

[dilalio]

I saw a reference to "I also fitted a 270lt tank with pump, so there is plenty of pressure/flow. There is already one thermostatic shower in place. See diagram for pipework."

Which did not sound typical of a combi.

But I see now it is a cold water cistern with pump.

After reading your cylinder colour question, I had to double check the OP first before replying. It's easy to miss the details in lots of descriptions if even included.

 

[dilalio]

Hi all, I have just fitted a new shower room with thermostatic shower and a basin. because our water pressure is awful I also fitted a 270lt tank with pump, so there is plenty of pressure/flow. There is already one thermostatic shower in place. See diagram for pipework.

The old shower works great with this setup, pressure is so much better than before.

The new shower never gets more than lukewarm, even with boiler set to 60 (max). I already replaced the thermostatic cartridge (see other thread haha) but still the same.

- With the shower off, the basin tap DOES get hot, then if you turn the shower on as well the shower starts hot for 30 secs but then both the shower AND basin tap go lukewarm.

- If the old shower is running, then I turn the new one on, the old one also goes lukewarm after a few seconds.

Is this some kind of balancing issue? See pic - The pipework from the tank is 22mm until it splits off to go to old shower, and new-shower-plus-boiler. All other pipework is 15mm. I took the cold feed for the new shower off from the boiler cold feed about 50 cm before the boiler as that was a handy place.

View attachment 366696

Isolate cold feed to combi and open various hot outlets (turn mixers to max temp) see if you get any flow of water from hots.

Edit... Also, check how many lpm you are getting from the new shower and then how many lpm your boiler can handle at a 35/45°C rise.

 

[davidjatt]

Thanks for replies all, had the family here so not done any troubleshooting for the last couple of days. I will do the tests mentioned above. It's weird because it's ONLY when the new shower is on that the problem happens, and all hot taps become lukewarm. Like the new shower itself is allowing the cold to push back into the hot.

I did wonder whether I got the H/C the wrong way round but the temp control works in the right direction, it just goes from cold to not-very-hot. I will swap them anyhow just to check!

 

[Madrab]

Like the new shower itself is allowing the cold to push back into the hot.

Could quite easily be that. Most new showers come with non return valves to make sure backflow doesn't happen but sometime they don't work/get jammed and then if there are unbalanced supplies then it can crossflow.

 

[davidjatt]

Sorry, back from xmas holidays, but this is more confusing (to me at least!)

I added a double check valve to the hot supply before the shower, to stop anything going back that way. No change. I turned the cold isolator that feeds the shower, just a bit, to reduce the pressure. Then a bit more, then a bit more, then with the cold completely off it's STILL lukewarm.

I then adjusted the isolator for the hot, and once I'd brought down the flow a bit, the shower was suddenly hot. Whacked the cold isolator to wide open, temperature still good.

So I don't think I can blame the shower anymore.

One possibility as mentioned above by @dilalio ... is the new combo of pump plus a new shower just allowing more flow than my boiler can heat at any given temperature? And the other shower is further away/somehow more restricted, so it is still OK? The boiler is actually just a water heater (i.e. no CH as I've got a heat pump for that) a Vokera easi-flow LE 30KW. I can't believe that a 30KW boiler can't supply one shower. According to the booster pump specs it will deliver 40l/min at 3 bar which is obviously quite a lot, and it's fixed speed. The boiler specs state 13.2l/min but I don't know what that really means... it will guarantee to heat water to 60 degrees at 13.2l/min? What if the flow is more, does it just try it's best but the pump just supplies more water than it can heat?

 

[davidjatt]

Oh.... Quantity of hot water with Δt 30°C = 13.2l/min. But, but... I had 2 showers in my old house and didn't have this problem. Seems like I need an industrial boiler to get it hot enough. Or do you always eventually need a hot tank if you want lots of hot water flow?