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Plumbing

Why can I only get hot water if I reduce the flow and how do I fix this?

Anonymous user 09/03/2024 - 3.07 PM

I have a combination boiler and the central heating in the house works fine. However, the hot water in one of our two bathrooms is problematic. It is an older property, a barn conversion from the eighties that was originally a pair of cottages that the former owner combined into one dwelling. The bedrooms and bathrooms are on the ground floor and the living area and kitchen are upstairs. We have a Veissmann Vitodens 100 combination boiler that was installed in 2013 (we moved here in 2016) and has been serviced every year. It appears to work fine. The problem lies with our 'guest bathroom'. It's been little used in the past three years. The toilet and sink get used, but the concealed thermostatic mixer shower and rarely do. The shower definitely did work properly when we first moved in; it was hot and plenty of pressure. We are unsure about the bath. A new addition to our household has meant the shower is now being used daily, however it is not getting hot. We are in the process of replacing the shower unit. However, as I removed the bath panel below the shower, I tested the hot water in the bath and realised that the pipe leading to the tap was not getting warm or hot when I ran the hot water which only came out moderately warm. I had thought that the mixer tap in the bath was broken, but the cold pipe indicates otherwise? I turned a little screw on the hot pipe and this had the effect of reducing the flow of water into the tap, and suddenly we could get very hot water. However when we played with this, we ended up with such a slow from that it would take forever to run a hot bath. I then turned to the sink and repeated the process and it was exactly the same. The only way to get hot water out of the bath and sink was to reduce the hot flow into the tap/mixer unit. I'm presuming the shower has the same problem, and that when we finish fitting the new one that this does not fix it. I'm pretty sure it hasn't been like this all the time as I remember being able to have a nice hot shower after we moved in. Our other shower works fine but that is electric. Also the other bathroom sink and kitchen sink both get nice hot water at good flow. I'm not a plumber, and nothing really about boilers/heating, but us this something obvious that could be causing this? Thank you in advance?

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4 Answers

As-Soon-As-Poss Plumber

Rating: 5 out of 5

Gosport

Hi Chat. Have you have had the boiler checked / serviced. Unfortunatly this time of year the mains water entering the combi is extreamly cold and would need more time to pass over the flame to heat it... thus slowing the flow has the desired effect but also in your case reduces the volume / speed of hot water through the tap etc. You likley know this, so it may help if the boiler was checked to see if more gas / energy can be delivered... often it's just a turn of a screw by a gas safe enginer that does the trick. For the shower, you could try as a quick fix replacing the shower rose for one that is smaller / less flow. Regards, Bob.

Answered19 January 2020

Sheriff Heating & Plumbing Services

Rating: 5 out of 5

Luton

Very good answers have been listed such as, secondary heat exchanger being problematic, diverter valve and of course extremely cold water supply taking longer to heat. Additionally, if your boiler is rated at, let's say, 12 liters per minute and your water pressure is great and providing 16 liters per minute then, hot water is affected. Considering the size of your property and the amount of bathrooms, it might be worth considering unvented system installation?

Answered28 January 2020

Anonymous user

I could only point it to a blocked due ( domestic heat exchanger). The problem with servicing a boiler it doesn't include checking the radiators, water conditions in the heating system or if the dhw is scaled. But this is common problem with combi boilers. It's probably best to get it checked, cleaned or replaced. If you look on YouTube and search blocked domestic heat exchanger you will have a better understanding. But it could be other things to like the run of the pipe, Is it insulated. Or even a faulty diverter valve. As if the diverter is faulty you wouldn't notice it in the summer as the heating is always running but would notice the issue in the summer.

Answered20 January 2020

Anonymous user

Hi yes I agree to all answers . I will add by checking the filter washers on all appliances to see if they also need cleaning .. SGS

Answered29 January 2020