I have a Chaffoteaux instanteous hot water system under the kitchen sink. Yesterday when I turned on the hot water taps in mid morning, hardly any water came out, but the cold water taps are working fine. A few hours later I turned on the hot water taps again, hot water came out as usual. Then after less than an hour, when I turned on the hot water taps, hardly any came out. I woke up at 3am and tried the hot water taps, hardly any water came out. This morning, hot water came out as usual for less than half an hour.

I called the plumber who thought it's the appliance. I checked with the appliance supplier and was told that even if the appliance is faulty, there should be still (cold) water coming out from the hot water taps.

The plumber is wrong and the supplier is right. If your heater failed you get cooler water at normal volume. You mat have some crud caught in the hot inlet on you faucet. Tell me about your faucet, brand and model if you can.

Thank you for your response. The problem is not confined to kitchen taps; it affects all hot water taps. We have a Hansa mixer in the kitchen, not sure about the hot water taps in the bathroom.

From last night until now, I have hot water from all the taps with reduced water flow; the water temperature is not as hot as before. Could you flow some light on why the problem is on and off?

Does this instant heater just handle the kitchen sink or is it piped to your other fixtures too?

The instant heater is the source of hot water supply to the kitchen and bathroom. There was no water from the hot water taps for a few hours yesterdays afternoon but hot water resumed at night. Maybe a faulty valve in the appliance is the trigger of this on-and-off problem?

I suspect that the cold supply to the water heater is the source of the fluctuating pressure. Does the heater have a drain spigot, if so try connecting a garden hose and open that spigot when there is low pressure at the sink. Tell us what you find.

Based on what you said, I'm pretty sure that the appliance needs servicing. Maybe there is a blocked venturi or faulty water governor. In any event, the diaphragm is almost due to be changed. I'll get the appliance people to come in instead of a plumber.

Many thanks for helping me.