Thermostatic Mixer Shower Valve with pumped hot water only

[helenpenny]

We've just plumbed in a thermostatic shower valve. It lets cold through no problem but no hot water gets through unless you trun another hot water tap on in the flat. The cold water is mains fed but all hte hot water in the flat is pumped. It seems as though the pump is not recognising that there is an outlet open for water to go through if that makes sense. Any ideas?

 

[doitall]

That's probably because there is no flow

The higher pressure cold is holding the hot off until the pump is running

 

[helenpenny]

We tried running it overriding the anti-scald thingy with just hot water running through by turning the cold off at the mains and tyurning as hot as it would go. Still no hot water comes through until the pump is started with another tap somewhere else. Don't really understand how the thermostatic valve works and I'm gaggin for a shower!!!

 

[doitall]

You can't over-ride the anti scald thingy.

No cold = no hot on most valves.

Does the shower work with the pump running.

If so to proof the point start the shower with another tap open, then turn that tap off when the pump kicks in.

 

[doitall]

On a seperate issue you have connected the valve the right way round.
And what make model is the valve

 

[cozzmic]

Correct me if I'm wrong , you can't connect a shower mains one side and pumped the other, unless there is some backflow prevention. Also I'm aware that you get mains cold, backfed hot through a venturi mixer (Trevi) but not pumped.

 

[helenpenny]

Ta for your advice.

The shower works OK with the pump running so if we leave another hot tap elsewhere running it's fine but as soon as we turn the other tap off teh pump cuts out within 30 seconds or so. The shower is an Amber Vienna twin control concealed thermostatic shower valve. There are non-return valves. We removed the non-return valve to the hot because there is already a non-return valve at the pump we think. Do you reckon it's the unbalanced hot/cold pressures then? If so, is there any pressure equalising device we could plumb in?

 

[doitall]

Its like I said catch 22 situation.

The pump needs a flow to start, and the shower needs the pump pressure to work.

An accumulater may work but wouldn't hold my breath

 

[helenpenny]

Presumably we need a shower suitable for different pressures or something? I understand what you mean about the catch 22 situation. It's weird that the pump stops working when the other tap is turned off even though the shower is apparently working...

Anyway, thanks again.

 

[helenpenny]

Would a pressure equalising valve make any difference do you think?

 

[chrishutt]

Might it be that the flow switch on the pump is not as sensitive to flow as it should be. Some are attached externally and can get moved out of the optimal position.

If you decide to change the shower valve, a venturi shower should work much better, perhaps without the need for pump.

 

[Gasman1015]

Had a customer with a similar problem using a bristan mixer, the hot supply was to weak to flow through the mixer, turned out there were restrictors inside the valve entry and once prised out the flow was sufficient to turn on the pump.

 

[ChrisR]

Agree with gasman here - look for ways to increase the hot flow. Try with the head on max flow - or maybe another head. Just to try it, have a go with the head taken off the hose.

 

[helenpenny]

Tried it before without the head and no difference.

I think perhaps the pump is not sensitive enough to flow because looking at other taps the hot water has to run at a fairly hefty rate before the pump kicks in.

I'm thinking perhaps of a better pump and then maybe a pressure equalising valve or a new shower that will cope with differences in pressure. What do you think?

 

[doitall]

What you could do if you can find someone with the neccessary skills is fit a flow switch to the shower cold.

This could be wired to overide the pump switch.

there i go again giving away trade secrets.