Thermostatic shower bar groans and pulses.

[EddieJT]

I've fitted a new bathroom and put in a shower cubicle. The thermostatic bar does not work very well, it's difficult to regulate temperature and it groans and pulses or nothing comes out at all.

The hot water comes from an old gravity fed system, and the cold is off the mains as opposed to the cold water tank (as it was easier for plumbing). Is this my problem? I've crudely used an isolator valve on the cold mains side to get the pressure down to the same as the hot, but I'm guessing this is not accurate enough?

Would a difference in hot/cold pressure give the symptoms I'm describing on a thermostatic bar?

 

[oldbutnotdead]

Dunno about those symptoms exactly but mismatched pressure will make the temperature control less accurate.
2 options;
1 Pipe the cold from the dhw header tank
2 Calculate the hot water pressure (10m vertical from water level in header tank to shower head = 1 bar), put a proper pressure reducing valve in the cold feed (about £25 iirc) and set it to the same pressure.
Also check that the mixer you bought is suitable for the pressure in your system (low pressure, likely to be less than 1 bar on the hot)

 

[Madrab]

Yes, that's your problem. A new style bar mixer shower will struggle with a gravity fed hot and mains cold.

You could try removing the NRV from the hot side and wind down the cold side until it runs but it will struggle to be correct.

All the valve will do is reduce the cold flow, the pressure will remain the same and may still restrict the hot from flowing properly.

 

[pete50]

I couldn't get my shower bar, installed 8 years ago by me, to work at all on just the pressure from my vented system. I had to install a pump that pumped both the hot and the cold water. That's works fine until the rock hard water in my area gums up the thermostat.

 

[EddieJT]

Might be easier to just fit a manual shower bar: https://www.amazon.co.uk/Shower-MOC...words=manual+shower+bar&qid=1608388761&sr=8-5

 

[Madrab]

You'll still have the same issue if using unbalanced supplies, the cold would always overwhelm the hot until they can be better equalised.

 

[JimCrow]

If you have access to the hot and cold pipes before the shower one of these,

https://www.bes.co.uk/water-pressure-equalising-valve-16711/

 

[EddieJT]

You'll still have the same issue if using unbalanced supplies, the cold would always overwhelm the hot until they can be better equalised.

Oh really? Glad I asked then.

 

[EddieJT]

If you have access to the hot and cold pipes before the shower one of these,

https://www.bes.co.uk/water-pressure-equalising-valve-16711/

View attachment 215173

Ah interesting. Yes I have plenty of access to the hot and cold pipes at the moment (pre boxing in). Do these work well then?

I've got to decide what's worse, going to the effort of routing a cold feed from the tank, or spending £25. Hmm.

 

[JimCrow]

Ah interesting. Yes I have plenty of access to the hot and cold pipes at the moment (pre boxing in). Do these work well then?

I've got to decide what's worse, going to the effort of routing a cold feed from the tank, or spending £25. Hmm.

If you can, the tank option is your best bet, these work but it is another restriction on your pipework you could do without if you don't have
a lot of head.

 

[EddieJT]

Yeah I think I'll bite the bullet and do it properly then by getting cold tank feed to it. I'll be gutted if I still have the problem though.

 

[Madrab]

I'll be gutted if I still have the problem though.

Once you have swapped to tank cold then the only issue you'll have is the pressure it can deliver.

Maximise the flow by kwwping the pipe bore at the largest possible unitl the last minute, remove the NRV's from the shower, use the largest bore shower hose you can get, MIRA hoses are the best I've found and get the highest flow shower head you can get.

If you have a cheap bar mixer then they tend to have narrow waterways. A good tip is to swap the 1/4 turn on and off flow valve for a normal screw down valve, they should be interchangeable.

 

[EddieJT]

Good tips.

As it is, I can get the cold to come out no problem and with a lot of faffing about I can finally get the hot to come through too. This is with lots of back and forth on the temperature knob, and lots of groaning and pulsing from the bar. Then it works well for a shower.

Leave it for an hour though and it's back to square one with no hot water coming through, without the above messing about. Does this sound like air in the hot water feed? Should I put a NRV on the hot water?

 

[oldbutnotdead]

No, it sounds like a massive pressure difference between hot and cold. If you balance the pressures there'll be no need for NRV in the hot (as it is yes it is possible that the cold is pushing the hot back up the pipe). The groaning & pulsing will be the innards struggling to sort the temperature out.
EDIT The reason for faff is the initial cold in the hot pipe and overpressure in the cold not allowing flow in the hot & thus hot water not making it out of the cylinder til you more or less kill the cold water flow

 

[EddieJT]

Ah ok.

I have another thermostatic shower at the same height but with a proper cold tank feed, and it works fine. So I'm hoping that bodes well for me not having a general low pressure problem. Soon find out.