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James I
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I live on the fourth floor of a 1960s council block. I have

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I live on the fourth floor of a 1960s council block. I have a combi boiler. I have never, ever had any problem getting good strong flow of hot water to both the kitchen and bathroom taps. However, the shower doesn't seem to fire the boiler. Often it just runs cold. It will work occasionally, but it's unpredictable. I think it might be worse during busy periods in the building, like around 10:30am on Saturdays or 8:30am weekdays, but I could well be imagining it as I'm racking my brains for a solution.
I had an electric shower before and I thought it might be a flow problem (hence my theory it might be worse at busier periods), so I replaced the shower with a new electric model to no avail. I've just had a non electric shower fitted and the problem persists!
The other day I decided to put the kitchen tap on so it fired the boiler. I left it running and tried the shower. I eventually got hot water coming through when I reduced the flow so it was barely running at all. I then turned up the strength and got a good flow of hot water, but it was only hot! I couldn't get any cold regardless of what I did with the temperature gauge. This also happened with the previous shower so is not unique to the new one.
I have no idea what's going on. How can the shower fail to receive hot water at exactly the same time the tap in the same room is working with no problems?? Aren't they both connected to the same system? Any help much appreciated. Thanks

This is a strange one, I would be inclined to remove the shower head and see if when the shower is turned on and water flows out of the hose if that starts the boiler.

The boiler is activated based on a flow rate, so it may just be the flow sensor is starting to fail as the shower head is restricted the flow rate compared to a tap, and a new flow sensor would be reasonably straight forward to replace on a boiler.

If its not the flow sensor, I dont think it should be affected by other people in your building. I would start by running the hot tap in the bathroom and shower (with the head removed) and see if the water is the same temp under both tap and shower, if they are not it suggest you have a mixer \ temp regulator which is mixing cold water with the hot before it gets to your shower mixer.

I cant see any other explanation for your issue, and would look to start tracing the pipes between the sink and the shower to see what the cause may be.



Customer: replied 1 year ago.
Hi, thanks for prompt response. I don't think it can be the flow sensor because I've tried three different showers - the one attached now has a very strong flow. What do you mean when you say a mixer/temp regulator? A thermostatic mixing valve? Where would I usually find that? In the bathroom or closer to the boiler?

A thermostat safety valve are designed to stop the temperature exceeding 40 degrees, they are normally located in bathrooms, to prevent scalding children in the bath etc.

The valve is often located under the shower tray or behind the bath panel so it can be serviced, most modern day mixer taps have built in thermostatic valves as well so it may be a failure on the mixer tap itself.

The valves look like the ones here and here

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