Thermostatic bar shower problem

[welshfella]

Looking for some advice regarding my shower. Its a thermostatic bar type supplied by a combi boiler. Recently it has started running cold after approximately 1minute. Suspected a cartridge issue. Rather than replace cartridge I replaced entire bar. I still have the same issue. It runs fine for about a minute and then goes cold. I've checked the boiler and it isn't calling for hot water. If I remove the shower head then I get constant hot water. I've replaced head and hose but have same problem. I presume I don't have enough flow to trigger the hot water demand. But not sure whats changed. All other hot water taps in house work fine.

 

[Ben-gee]

Get yourself a high flow head and it should be fine.

 

[welshfella]

Thank you for the reply Ben-gee. Tried a high flow head (at least i think it is, screwfix don't market it as high flow but amazon do) still the same problem. I have found though that If I start to draw hot water from the bath tap, then turn the shower on, then turn bath tap off I get constant hot water in the shower. Not sure if I read that on this forum or another. Could it be a problem with my water supply?
Thanks for the help.

 

[king of pipes]

Looking for some advice regarding my shower. Its a thermostatic bar type supplied by a combi boiler. Recently it has started running cold after approximately 1minute. Suspected a cartridge issue. Rather than replace cartridge I replaced entire bar. I still have the same issue. It runs fine for about a minute and then goes cold. I've checked the boiler and it isn't calling for hot water. If I remove the shower head then I get constant hot water. I've replaced head and hose but have same problem. I presume I don't have enough flow to trigger the hot water demand. But not sure whats changed. All other hot water taps in house work fine.

Our sponsorl has products to solve your problem. Regards kop

 

[John.g]

Looking for some advice regarding my shower. Its a thermostatic bar type supplied by a combi boiler. Recently it has started running cold after approximately 1minute. Suspected a cartridge issue. Rather than replace cartridge I replaced entire bar. I still have the same issue. It runs fine for about a minute and then goes cold. I've checked the boiler and it isn't calling for hot water. If I remove the shower head then I get constant hot water. I've replaced head and hose but have same problem. I presume I don't have enough flow to trigger the hot water demand. But not sure whats changed. All other hot water taps in house work fine.

Could be mains water pressure reduction or a problem with a PRV if fitted or some problem with the cold water supply only to the shower, the shower flow switch should be more than happy with a flow rate of 3 lpm which then only requires a cold water flow rate of ~ 2 LPM to give you a comfortable showering temperature of 40C and it would be a very restrictive shower head that couldn't flow even 5 LPM without a large pressure drop, also the original shower worked OK so if both that and the new installation are giving problems it might point to some problem external to the shower even though hot water taps run OK. You might measure the flow rates through the shower head when turned to fully cold & fully hot & the normal mixed flow position to give you some idea of the problem.
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Meant "combi flow switch" not "shower flow switch" above.

 

[Ben-gee]

He said it works fine with no shower head, this indicates that if a high flow head (ie one with low back pressure) were to be used then the shower would work.

 

[John.g]

He also said it worked with a shower head originally!
"Recently it has started running cold after approximately 1minute "
Maybe he should try the original shower head, he may have as he said he originally replaced the bar.