We had a loft conversion done a few years ago. As part of this we had a thermostatic shower (bristan quadra) put in the loft ensuite and and a bar thermostatic shower put in on the first floor. These are both fed by a 2 bar ( I think) pump which is next to the hot water cylinder on the first floor. It took a while to get all the tiles done which probably did help matters. Plumbers subsequently got fired by the conversion company.

As such the loft shower never quite gets hot enough. It’s fine for me if no one else has used the hot water but not hot enough for my wife. Conversely the shower downstairs is generally too hot. If you turn the temperature down the shower just shuts off its flow. You can then restart the flow by increasing the temperature knob and trying to tweak it slowly down so you don’t get scalded.

Any thoughts?

I’m no plumber, and somebody will no doubt correct me, but I have had problems with a thermostatic shower in the past.

Thermostaic showers have an adjuster inside, you’re supposed to get a thermometer, run the shower at a set temp, and tweak the adjuster until the thermometer agrees with the temp you’ve set it at. ‘Calibrate it’ if you like.

Many of these showers also require a set input pressure to both hot and cold feeds, you have to use pressure regulators to make sure they’re in the right range.

Sounds like good advice.

You could fit a second pump for the loft shower, to boost the HW pressure.

Sounds like it could be a flow/pressure differential at the pump inlet. The hot and cold feeds to the pump should be at the same pressure, if not, you will always get more of one than the other.
The downstairs being too hot suggests a flow problem, too little hot, or too much cold, with the shower mixer not being able to moderate the flow correctly.
If possible, can you take some pics of the where the hot and cold water leaves the tank/header tank, then that can be discounted if not that.

Upstairs could be limted by the pumps capacity, but I suspect an unbalanced flow into the pump.

Thanks for the input, I usually have a go at most DIY stuff but I think it’s time to call in an expert.

Where are you?

North Hants.

Too far for me to look at.

Thanks anyway.

If you have tank feed hot and cold and a double impeller pump the pressure of the hot and cold water to the pump will be equal and if the pump is feeding a shower remotely, I’d guess that’s how it’s set up. Sounds to me like neither shower was ever commissioned properly. However, it never pays to guess what a plumber might do. You need the help of a good plumber. Good luck with that.

Most thermostatic showers have a maximum temperature stop built into the temp control knob as a safety feature. If this has been set too low on your loft shower you will not be able to get the outlet temperature up despite a high hot inlet temp.

2 bar pressure from the pump should be fine, however depending on the pump type this can drop rapidly as the flow rate increases. Regardless you should be able to achieve a higher temperature regardless of flow rate unless you have emptied the hot cylinder.

I would start by removing the temperature control knob on the loft shower and looking for the max temperature stop. This is usually a mechanical stop fitted to the splined shaft and between the outer knob that can be adjusted to allow greater or reduced rotation and therefore temperature.

Search the internet for the Installation and Maintenance instructions for the shower valve, that should contain details.

Much appreciated, I had hoped it might be something like that. The upper shower is the one I am more worried about. I will have a look at the inner mechaism. It does get slightly hotter if you tweak the hot water thermostat up to 65 deg or so but with kids that is the safest thing to to long term. Other odd thing is that it is slow to come on but comes on instantly if you turn on the hot water tap in the room?

The lower shower is absolutely fine when the hot water tank is not up to temperature so I guess the problem is a flow imbalance one.

I loved that plumber!!

It might be the thermostatic cartridge in the shower. If they fail they tend to let too much cold through. Bristan showers tend to have a 5 year warranty but they’ll want a receipt before they send you a replacement. All the spares are listed on their website, bristan.com

Is the shower head above the level of the cold water storage cistern?

Shower head on the loft shower (the one that doesnt get hot enough) is probably 30 cm below cold water storage.

Andy,

The delay in the shower coming on is possible down to the flow switch which starts the pump.

You usually only have a flow switch on one side of the pump and it requires a certain flow rate to activate. If yours is on the hot side of the pump turning the hot tap on would give more flow than the shower (because it’s got a greater head of pressure and is probably less resistive to flow). Flow switch activates, pump starts, shower…..

Peter, thanks that makes sense. Never really had a problem with that bit (due to the position of the shower it actually helps because you don’t get a cold soak on turn on) but being able to explain it to a buyer if we ever had to sell the house is a help.

The chances of the hot tap relying on the pump are very slim. In most cases only the showers are pumped because the hot tap is low enough on the system to work with gravity. The pump needs only a very small flow rate to start up and it will be either on or off. I would start as previously stated by checking the commissioning procedure which includes setting maximum achievable temperature. This is something you can probably do yourself at no cost.. All other responses are making unnecessary assumptions and over complicating a simple step troubleshooting process. Once you establish that it has either been set properly or not, you can then resolve it or move on to the next least expensive step. Replacing the thermostatic cartridge. Again, if the valve is less than 3 – 5 years old and a major brand, you have a good chance of replacing that under warranty. Also something you may be able to do yourself. Then follow the commissioning process again to set maximum temp.

Pump won’t start as outlet above tank therefore you need a negative head pump. Whether this is the cause for the shower malfunctioning is unlikely.