Mixer tap mystery - water flow problems

[Bob Moore]

The previous mixer tap developed a leak.
I ordered an exact replacement.
The hot &cold tails were too short so I had to replumb the water connections.

The new tap exhibited strange symptoms:-

In the fully open hot position no water flows.

The only way to get the hot to flow is to reduce the cold supply to a trickle.

I asked the supplier for a replacement tap and fitted it, but the results were the same.

The hot supply is fed up and through the loft and down to the tap in the kitchen, by a salamander pump.

The only difference in the plumbing is that two washers, which were in the supply were removed.

Unless I've been supplied with two faulty taps I can't understand what is wrong.

I would appreciate any suggestions.

 

[oz-plumber]

Pull out spray tap.
Could be the non-return valve not having enough pressure from the hot to open it.

Plus the tap will have flow restrictors, you mah have to remove or manipulate them.

 

[snowhead]

As above, it would seem that higher pressure in the cold is keeping a non return valve on the hot side closed.

How did the pressure on Hot and Cold compare on the old tap?

Does the Hot flow if only the hot side is open?

Can you post a picture of the pipework connecting to the bottom of the tap.

It's unlikely you have 2 faulty taps, it's unlikely either were faulty.
Unless you fitted the original and know different then I'd suggest whoever did fit it has posssibly removed a non return valve to get the tap to work.

 

[Bob Moore]

As above, it would seem that higher pressure in the cold is keeping a non return valve on the hot side closed.

How did the pressure on Hot and Cold compare on the old tap?

Does the Hot flow if only the hot side is open?

Can you post a picture of the pipework connecting to the bottom of the tap.

It's unlikely you have 2 faulty taps, it's unlikely either were faulty.
Unless you fitted the original and know different then I'd suggest whoever did fit it has posssibly removed a non return valve to get the tap to work.

Hi
Thanks for your reply.

There were no no return valves on the original plumbing.

I carried out the plumbing.

I had a plumber look at the problem and concluded that it is a problem with the mixer tap.


He suggested the tap is not suitable for the mains cold and the pumped hot.

So are there different designs of mixer taps and if so how do I know which type would be suitable to overcome this problem?

 

[Bob Moore]

Pull out spray tap.
Could be the non-return valve not having enough pressure from the hot to open it.

Plus the tap will have flow restrictors, you mah have to remove or manipulate them.

Could this be solved by inserting a non return valve in the hot feed?

 

[Bob Moore]

Could this be solved by inserting a non return valve in the hot feed?

Placed a non return valve in both the hot and cold feeds. Still not solved.
I can only assume the tap is in compatible and different to the original.
My question is, are there different types of mixer tap? What are they called? I don't want to replace the tap and find I have the same problem.

 

[Timmy D]

Get a kitchen tap designed for low pressure systems. They will work on low hot pressure/high cold.

Or adding a pressure reducing valve to the cold and reducing the pressure to match/slightly lower than the pump output will likely work.

 

[Bob Moore]

Get a kitchen tap designed for low pressure systems. They will work on low hot pressure/high cold.

Or adding a pressure reducing valve to the cold and reducing the pressure to match/slightly lower than the pump output will likely work.

Thanks

 

[Bob Moore]

Get a kitchen tap designed for low pressure systems. They will work on low hot pressure/high cold.

Or adding a pressure reducing valve to the cold and reducing the pressure to match/slightly lower than the pump output will likely work.

What psi is defined as low pressure?

 

[Ben-gee]

Low pressure is 0.2 bar which is about 3 psi.

You could solve the problem by changing the pump to a negative head one (often called universal nowadays).

Alternatively change the tap to one with a dual flow spout, the hot/cold do not mix in the body of the tap- it only gets mixed as if exits the spout and therefore the cold and hot can be at different pressures.

However you won’t get the pullout spout with a dual flow spout tap. So if you want to retain this functionality I would change the pump.

 

[Bob Moore]

Low pressure is 0.2 bar which is about 3 psi.

You could solve the problem by changing the pump to a negative head one (often called universal nowadays).

Alternatively change the tap to one with a dual flow spout, the hot/cold do not mix in the body of the tap- it only gets mixed as if exits the spout and therefore the cold and hot can be at different pressures.

However you won’t get the pullout spout with a dual flow spout tap. So if you want to retain this functionality I would change the pump.

Thanks for the info