Shower Temperature


29 Jun 2006
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United Kingdom
We have Bristan Prism shower which is fed by a Grundfos twin impeller automatic shower pump. The cold feed to this is from the tank in the loft and the hot feed is via a Grundfos Surrey Flange attached to the hot water tank.

We recently had to have the thermostatic cartridge replaced to try and overcome a longstanding problem with the flow of water starting to pulse/judder and then stop completely once the temperature control was turned to anything more than lukewarm.

I'm pleased to say that this does seem to have solved the problem and that we are now able to enjoy hot showers once again with a typical water temperature of around 38 degrees centigrade. However the characteristics of the new temperature control seem to be somewhat different to the previous one in that there seems to be little apparent variation in temperature wherever the temperature control is set, even though the tank stat has been reset at 60 degrees centigrade.

In addition we've noticed that when the temperature control is turned up towards maximum the flow of water will start to reduce and then increase again once the temperature control is turned down again. We assume that this is because there is some sort of restriction built into the thermostatic cartridge to prevent very hot water potentially being supplied at near to maximum temperature.

Obviously we're very pleased that the shower appears to working properly again but would be very grateful for confirmation, or otherwise, that the characteristics of the temperature control are now as they should be.

Many thanks, GSD.
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When you replace the shower valve cartridge it must be calibrated - the calibration is the relative position of the knob on the spindle.
Many thanks to seco services and Axel for getting back to me and I can confirm that I did indeed check the pump filters which were completely clear.

As far as the calibration of the cartridge is concerned I can confirm that the 'off' position of the temperature control knob is in the vertical 'noon' position, which is in line with the appropriate mark on the shower bezel. However if I've misunderstood this please don't hesitate to let me know.

I hope that this helps, GSD
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the off position is on the flow control not temp control.
the max temp can be adjusted by the thermostic cartridge.

have you the instructions for it ?
I'm afraid not - these were retained by the plumber who fitted it. GSD
I don't have a picture but the shower is a Bristan model PM SQSHXDIV C. The bill for replacing the cartridge quotes SKBQ 1503-973C as being the part number used.

The plumber told me that as far as he was aware the thermostatic cartridge didn't have any adjustment so all I really want to know is whether the new cartridge is working in the way it should.

Many thanks again, GSD.
i'll check the number but most have have adjustment for the max temp stop. ;)
to me sounds like a restriction on the hot.

PM me your email i'll send you instructions. ;)
Thanks very much for this but how do I send you a PM, which I presume means Personal Message?

Many thanks again, GSD.
Thanks very much for this from which it's quite clear that there is a way to adjust the maximum temperature of the shower. I'll either try to do this myself or contact the plumber again.

You've been most helpful, GSD

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