Cold shower

[Psyclist]

Ok this is a question about my shower at home.

Our boiler isn't the best and we haven't been happy with it for a while but we have the service plan from ****ish Gas and we ask them about the fact the boiler takes so long to heat up hot water and if you turn it to full flow, it seems to go cold again.

Anyway we've dealt with it for four years now, but all of a sudden we've recently found that the shower has gone cold. I know the weather is obviously cold, but we've never had this problem before at winter and it was still reasonably warm outside when this first happened.

Under normal operation, if we turn on a hot tap, after a not so short while, the water does get hot. At the moment the water is hot enough that if you run it slowly enough it is too hot to handle, but if we increase the flow a little with the tap it levels out at a more manageable temperature, but if we completely open the tap, it's just warm.

I like a cold shower, but it doesn't seem to matter what we set the Bristan Artisan (4 years old) at, we cannot get it to warm up unless we run the cold tap in the sink while the shower is running, then it gets a little bit warmer.

I bought a new shower valve off the net and just fitted it when I got home from work this evening. It is a vast improvement, but I still wouldn't say the water gets hot, even if I turn the valve right up in temp.

Anyone got any ideas?

 

[andrekhoury]

hello there i was analyzing your problem, actually im not english so i have no idea how is ur system plant is anyway, the problem is easy , ur heating surface is small meaning u have scale in ur boiler water side so the heat transfer is slmaller thats why u couldnt get enough hot water when u open the tap at max , u can make sure if whats im saying is true
usually when u dont have enough heat transfer , ur boiler heats up faster and the thermostat shuts it down , if i am right ur boiler tgemperature rizes faster then before before it heats the coil inside not the water cos of scale u need to clean using an anti scalant i hope my info was abit binificiary

 

[Psyclist]

Thanks for your response, I can just about understand what you mean.

Can anyone confirm this and if so, how do I go about de-scaling the hot water coil in my boiler?

The boiler is a Vokera Linea though exactly which model I cannot find.

To be fair, we are busy getting plans etc for a new kitchen and were thinking of replacing the boiler just because we've had so many problems with it, but if I can get it to work until we get the kitchen sorted that would be brilliant.

 

[Psyclist]

Can nobody else suggest anything at all?

 

[whydelilah]

I'm no plumber but I've had a not dissimilar problem and after much investigation this is what I've concluded.

I also have Bristan shower, a thermostatically controlled Prism that controls the temperature for the shower and bath; and a Worcester Bosch 24i junior combi boiler.

Firstly, my understanding of combi boilers is that they guarantee a certain temperature rise at a certain flow of water. Mine is 40oC at 8.6 litres per minute.

If you reduce the flow you will get a greater temperature increase, increasing the flow you get less. So, for example, if you turn the tap down so the flow of mains water through the boiler is 7.0 litres per minute you will get a greater temperature rise so the water is hotter. If you have it fully open and the flow is greater than the specification of the boiler (i.e. in my case more than 8.6 litres per minute) then your temperature rise will be less and it will be cooler. So you may be able to increase your hot water by reducing the amount that comes in through the mains to the boiler.

The reason (if my logic above is correct) that you get warmer water by running the cold tap is that by drawing off water from the mains you are reducing the flow through the boiler and the temperature therefore rises.

An added complication is that thermostatic cartridges require the blend temperature to be 10oC below the inlet hot water temperature. So if it's cold outside then the mains temperature may only be 5oC, therefore the maximum the boiler can raise it to is 45oC (depending on flow rate), but the maximum blend temperature you'll get through the shower is 35oC.

I would love for a more qualified person to comment on whether this logic is correct. I have no chance of a hot shower in winter based on the specs of my boiler (and it doesn't help that the Bristan Prism thermostatic cartridge has bust... again) and as I see it the only option is a higher spec boiler.

I can't comment on the internal working of the boiler but if your water supplier has kindly granted you an increased flow of water it may account for the temperature changes you're talking about.