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Gas Works

Erratic System Boiler ! Very Hot water and various ON/OFF cycles.

Anonymous user 23/02/2024 - 3.53 PM

I have a Vaillant SYSTEM boiler approx 13 years old and linked to a Nest Thermostat. Two observations suggest something is not quite right! 1.Recently, the domestic hot water has been very much hotter than usual even though I have Not changed any of the settings. Does this mean that a valve might be stuck somewhere and that the water might be being double boiled?? ( I have turned down the thermostat on the water tank and it still persists). 2.When the Domestic Hot water & Central heating programmes are turned off, I hear the boiler turning on/off during the night at different times. I appreciate that the boiler would need to turn on to get the Hot water tank ready for use for the morning programme, but I can’t understated why it needs to turn on/off at least 3 or 4 times during the night when the weather is not cold and the tank is lagged. Any ideas or remedies would be appreciated. Many thanks.

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3 Answers

YELLOWSTONE SERVICES LTD

Rating: 5 out of 5

Manchester

Firstly I would be looking at the cylinder thermostat- if it is faulty it can demand heat constantly. and make sure the programmer is on timed NOT constant. It would take 3,4 tests to pinpoint the problem- you do need a gas engineer to inspect , identify the cause, and fix.

Answered11 October 2023

Samson Plumbing Heating & Electrical LTD

Rating: 5 out of 5

Hythe

Hi there, Nest, as standard have a legionella function which will override your other controls and increase the temperature in your cylinder to 65 degrees C, killing off the disease. You'll know when the stat is in "Bacteria Prevention" mode by the non solid flame (below the room temp reading) on the Nest. This is typically after more than 2 hours of no heat demand within a 48 hour period, but that may not rule out a potentially faulty Nest. Dependent on the model of Vaillant system boiler in situ, a pre-heat function may be activated, constantly trying to raise the temperature inside the heat exchanger. Hence the constant cycling of the boiler. There may not be a problem at all. But, if you are unsure, reach out to a professional.

Answered11 October 2023

Mahmood Beigi

Rating: 5 out of 5

Northampton

Firstly cylander sat to see if that is faulty ,not reading correctly temperature

Answered5 October 2023