Combi boiler not igniting in some cirumstances

[BotchItYourself]

My combi boiler does not respond to the hot tap in my kitchen when my central heating is off. It responds slowly when the central heating is on. So in order to wash the dishes, I need to make sure the heating is on. The pressure from the tap generally feels low.

I have no problems with the hot supply to the bathroom which responds normally whether the heating is on or off.

What is the problem ? Is it the kitchen tap itself or is something wrong with the boiler ?

 

[ollski]

Hot water diaphragm I expect (edit, didnt read second paragraph. RTFQ)

 

[nortonj]

Is the flow from the kitchen a lot less than the bathroom.
Maybe not activating the flow sensor

 

[omega015]

Is it a mixer tap or separate hot/cold?
How hot is the water in the kitchen when heating is on compared to the bathroom with heating off?
How low is the pressure from the kitchen tap? (how long would it take to fill a litre jug)

Possibly flow sensor or tap is restricted and the boiler is not detecting enough flow to fire up (and your getting some heat due to heating being on)

 

[BotchItYourself]

The kitchen tap is a mixer tap.

The hot flow in the kitchen is noticably less than in the bathroom. I haven't timed it for a specified volume though I can do this at the weekend (I'm writing this at work).

The cold flow in the kitchen is OK.

The hot water in the kitchen when the heating is on is comparable in temperature to that in the bathroom with the heating off though it takes longer to reach full temperature.

 

[muggles]

What make and model is your boiler?

 

[Agile]

So many words to describe flow rates.

Sadly none of much use compared with a flow rate in litres per minute.

Tony

 

[Doggit]

It's very possible that you're heat exchanger is clogged up with calcium, and need descaling. That's why there's insufficient flow going through it to activate the boiler.

 

[BotchItYourself]

The boiler is a Worcester-Bosch 28 SiII.

The flow rate from the hot kitchen tap is approximately 2.3 litres per minute.

 

[DaveHerns]

Give the tap a going over, new washer etc, and report back.

 

[omega015]

Does the cold water pressure/flow from the mixer tap seem ok? Does your mixer tap have flexible hoses under your sink that connects to your copper pipes? Do you also have some valves to isolate the water to them? If yes to those questions, rather than taking your tap apart you could isolate the water, swap over the hot/cold hoses and see if the hot water pressure is any better and if its gets hot without the heating on (from the previous cold tap). If that works then its likely the tap has an issue.

 

[Agile]

The boiler is a Worcester-Bosch 28 SiII.

The flow rate from the hot kitchen tap is approximately 2.3 litres per minute.

Most boilers need about 2.5 litres per minute to turn on the hot water delivery process reliably.

Tony

 

[BotchItYourself]

The cold water flow from the mixer tap seems OK.

I have isolation valves but not flexible hoses and so do not have the ability to easily swap the pipes.

 

[Agile]

And presumably you have checked the hot iso valve is fully on?

A little trick is to turn hot tap on and watch flow rate as you turn the iso valve as sometimes the maximum flow rate is slightly different from the optically expected position.

Tony