Intermittant hot and cold water from Ravenheat combi boiler

[KKPP]

Hi, I have a Ravenheat White Star LS80 combi boiler, the problem is that it is not giving me constant hot water.

The problem started sometime last year when occasionally whilst having a shower the water would suddenly go cold.

However recently the problem as got worse and now it rarely gets hot.

I made sure this wasn't caused by other taps or appliances being used, as the problem stilled occured when nothing else was using the water supply.

The boiler seems to work fine - fans seems to go on etc - and when the hot water goes on you can hear the flames fire up inside. However without touching anything - and leaving the same flow at the tap - I can hear the gas flame switch of inside the boiler and therefore I loose the hot water. However the boiler fan etc still seems to be working fine.

Initially the problem was worst in the morning when I found I had to turn the heating on to allow the boiler to get started. Now however even that doesn't seem to work.

The same problem of the flame switching on and off has also started occuring with the heating system.

I feel this should be a simple problem to solve but my knowledge of boiler systems is somewhat limited.

Could anybody help?

 

[Agile]

There are several possible causes but rather than just list them all which achieves nothing a first simple test would help.

Its amusing that so many consumers who call us say that they think that its something simple! What they really mean is that they hope that it will not be expensive.

If you run a bath hot tap full on then does the boiler still cut out and what is the flow rate in litres per minute?

Also how old is the boiler?

Tony

 

[KKPP]

Hi Tony

Thanks for your help.

Ok I'll try to answer your questions best as I can.

There is no bath in the flat but I've run the tap to the kitchen sink (which is right next to the boiler). I've tried it full on and although boiler starts making a noise, which I think is the fan, there are also other noises which make me think something else is trying to start up. Occasionally the gas fires up inside the boiler and then after a few seconds it stops, giving me hot water when it is on and back to cold when it goes off. A similar thing happens when I try using the heating or shower, or a combination of the outlets.

Initially I used to get hot water most of the time and occasionally it would turn cold, but now it's more often cold then hot.

The boiler is about 1.5 years old.

There are several flow rates in the manual. I'm not sure which is the required one so I'm putting them all down.

DESIGN FLOW RATE 1033 l/h 20degC (17.2 l/min)
MINIMUM FLOW RATE C.H. 650 l/h (10.8 l/min)

D.H.W FLOW RATE 30degC rise 11.5 l/min
D.H.W FLOW RATE 35degC rise 9.9 l/min
D.H.W FLOW RATE 40degC rise 8.6 l/min

D.H.W MINIMUM FLOW RATE 3 l/min

The flat shares it's water supply with 2 other flats but this problem never occurred until at least 6 months after installation, and there has never been any problem with any of the other boilers in the other flats (the boilers are of different make).

The boiler is a Ravenheat White Star 24T - LS 80T

I hope I've supplied enough info. Let me know if you need anything else.

Kevin

 

[ChrisR]

Erm yes we know what the manuals say!
WHat is your actual flow rate of HW - measure it in a jug or bucket to get a figure in litres/minute, like 4 or 8.

 

[KKPP]

With the kitchen tap full on I got 8.8 l/m.

Do you need the flow at the shower point as well?

 

[fela kuti]

water flow seems fine all though a little low.
confirm that fault is common to central heating and hot water.
if 1.5 years old unlikely to be mechanical fault.
at a guess gas valve, avp or pcb

 

[doitall]

If I knew anything about bake bean cans I would go for the DHW Sensor, followed rapidly by the DHW Potentiometer.

 

[Agile]

OK with the kitchen tap on full thus giving 8.8 li/min.

Please time how many seconds the gas burns for followed by how many seconds its stays off for.

So far I have no reason to think that its not dirt in the heat exchanger.

Tony

 

[mavric130778]

I also have a whitestar combi boiler and have the same problem. I try to run a hot bath and have no joy at all. The flame seems to light up inside the boiler but only or a very short time. From reading the above i have to say i dont get anywhere near as much hot water, between cold water i usually get about 8 pints thats if i am lucky its usually less. I have never had a combi boiler before and i really get quite wound up about it not working corectly. When i first moved in the house i used to be able to get a hot bath but the tap would have to be running really slowly and it would take 40 minutes to run now it takes even longer and is rarely warm. Someone please help.

 

[gas4you]

OP; I would say it is overheating and shutting down till it cools. Could be system side sludged up or DHW side scaled if you live in hard water area.

Possibly could be the ch thermistor faulty, but would look at the above 2 first.