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Plumberpro, Plumber
Category: Plumbing
Satisfied Customers: 634
Experience:  Heating and plumbing answers. 20 years experience
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There,I have a Combi boiler (Vaillant Turbomax Plus

Customer Question

Hi there,
I have a Combi boiler (Vaillant Turbomax Plus 824 E or 828 E - I don't know which as can't find it written on the boiler itself).
I have a shower that, up until the last month, ran really hot all the time, regardless of whether the heating was on or off. I couldn't have the setting anywhere near hottest because it would've been way too hot.
About a month ago, something changed. My shower now runs nice and hot for about 90 seconds then, even at the hottest setting, goes tepid. It then cycles between nearly cold and luke warm.
I noticed the water pressure was low on the boiler (0.5 bar), so I filled it back up to 1.5 using the built in valve. This hasn't helped.
Hot water has always cycled between hot and luke warm when running the taps in the house but the shower has been fine.
Any ideas on what this could be?
I have minimal DIY skills - is this a job for a gas engineer?
Submitted: 2 years ago.
Category: Plumbing
Expert:  Plumberpro replied 2 years ago.
Hi ,the domestic heat exchanger is sludged and or its scaled.and holding back the flow through it. This results in what you are experiencing. The boiler gets up to temperature but overheats as the water is not flowing through fast enough, then restarts and continues this process of on and off, hot and cold.Change the domestic hot water heat exchanger