cold water in shower diminishes by itself

[RamJacCorp]

Tried posting this in USA forum, but I don't think it posted. I have an old Delta 3-handle shower/tub faucet. After replacing all 3 valve cartridges, when I set the temperature and flow I want, the cold water very slowly reduces, all on its own. I used silicone when I installed the new cartridges. This is not a pressure balancing faucet. What could be causing the cold water to keep diminishing? Any idea how to correct this? Here are the cartridges:

 

[RamJacCorp]

No one has a thought about this issue, huh?

 

[ShaunCorbs]

All the other taps ok ?

 

[RamJacCorp]

All the other taps ok ?

Yep, everything else works fine. The only symptom is that the cold water slowly decreases, and I have to keep turning it back up. Crazy.

 

[ShaunCorbs]

Yep, everything else works fine. The only symptom is that the cold water slowly decreases, and I have to keep turning it back up. Crazy.

Turning what back up ?

 

[RamJacCorp]

Turning what back up ?

The cold water, after it decreases all by itself.

 

[Chuck]

The cold water, after it decreases all by itself.

Can you touch the cold supply pipe at a point reasonably close to the shower? If so, while the 'cold is decreasing all by itself' does the cold pipe get warm?

While the 'cold is decreasing all by itself', does the flow rate (litres/minute) from the shower outlet decrease or remain constant?

 

[RamJacCorp]

Can you touch the cold supply pipe at a point reasonably close to the shower? If so, while the 'cold is decreasing all by itself' does the cold pipe get warm?

While the 'cold is decreasing all by itself', does the flow rate (litres/minute) from the shower outlet decrease or remain constant?

Thanks for the helpful questions! I'll have to get back to you on the first one. As for the second question, yes, the flow rate slowly drops, which is how I originally figured out that it was the cold water decreasing, and not the hot water increasing.

 

[Chuck]

Thanks for the helpful questions! I'll have to get back to you on the first one. As for the second question, yes, the flow rate slowly drops, which is how I originally figured out that it was the cold water decreasing, and not the hot water increasing.

I'm envisaging an arrangement that has a valve that diverts flow either to the shower head or to the bath tub. If so, does the same problem affect the outlet for the tub?

Is the cold water supply fed from a storage tank or directly from the mains supply?

If it's from a tank, have someone watch the level in the tank while the shower is operating. It may not be filling fast enough, e.g. because a valve has been left partially closed.

Also, have a look for mesh filters in the pipework that supplies the shower.

 

[RamJacCorp]

I'm envisaging an arrangement that has a valve that diverts flow either to the shower head or to the bath tub. If so, does the same problem affect the outlet for the tub?

Is the cold water supply fed from a storage tank or directly from the mains supply?

If it's from a tank, have someone watch the level in the tank while the shower is operating. It may not be filling fast enough, e.g. because a valve has been left partially closed.

Also, have a look for mesh filters in the pipework that supplies the shower.

Yes, the center knob is the diverter valve. That cartridge was replaced, along with the hot and cold valves. I just tested the flow from the tub faucet, and it didn't seem to get warmer. When I switched to the shower this time, it actually behaved normally. First time it's done that, (kind of like when your car makes a noise, but it stops as soon as you bring it to the mechanic), so I'll have to repeat that test a few more times.

The cold water supply is direct - no tank involved.

The pipes are original, from 1960. No sign of any mesh filters. Faucet was replaced around 15 years ago.

Thanks again for your help, Chuck.

 

[Chuck]

The cold water supply is direct - no tank involved.

Am I correct to assume that the hot supply is from a straightforward unvented tank or does it come from a combi boiler?

 

[RamJacCorp]

Am I correct to assume that the hot supply is from a straightforward unvented tank or does it come from a combi boiler?

The hot water comes direct from a standard gas water heater (tank type, not on-demand).