gas water heater problem - no hot water - help!

[pm99]

Anyone got any ideas....

i have a gas water heater on the wall....heats hot water for drinking and radiators.

Past coupld fo days soemtimes there would be hot water sometimes not.
If there was hot water in the bathroom there woudl be none in the kitchen...and vice versa...very irregualr pattern.
Now there is no hot water at all.
The gas heater is the type that heats the water as it passes through (ie no storage tank)....and the pilot light does not come on when i turn the hot water on.

A few days ago i connected up the sink taps for the first time since moving in several months ago....a couple of days later i started having the problem.

Is it possible i have got air int eh system so it is not recognising the water flow in hot water pipe?
Do i need to slightly drain the heater. The heater is the highest point in the system....so how do i get any air out if that is the problem?

Any help much appreciated!

[parrot of doom]

The pilot light should always be lit, otherwise you'd never be able to light the gas.

First thing I'd suspect would be the thermocouple.

[D_Mike]

use the kettle? (sorry)

[dirkgently]

Sounds like the flow switch

Any details make model ECT

[wacky racer]

Ferg!!!!

[wacky racer]

parrot of doom said:

The pilot light should always be lit, otherwise you'd never be able to light the gas. First thing I'd suspect would be the thermocouple.

That's what I thought, although I know all.

If it is the thermocouple, they are usually cheap and easy to replace.....

[pm99]

thanks for the replies so far...
the pilot light is only supposed to go on when there is flow...it is supposed to start up when you turn the hot tap on...
i thought it might be somat like a flow meter....wondered if i had done damage when putting new taps on as that would have emtied the heater of water etc. Likely?

The model is a french model.....therma plus...that's all i can find.

Any idea if a flow meter is easy or expensive to replace etc?

[z4monster]

It could be as simple as a microswitch. My boiler has a valve which opens when you get water flow past it. It then presses a microswitch which fires the boiler and you get hot water. My switch was dodgy and so sometimes you got hot and sometimes not. Mine's a Vailant boiler so yours may not have the same mechanicals.

[dirkgently]

First check the pressure in the central heating system it should be one bar (aprox)

With the selector switch/thermostat in winter position and turned to maximum does the boiler fire for C/H?

If yes

Is there at least 3 litres /min water flow at taps?

If yes it is probably the water valve diaphram or the microswitch

[Father Ted]

My nan's water boiler had this problem recently ,pilot light wouldn't stay lit ......started as an intermittant problem that turned into a full blown 'hard' fault.

In this case it was the pilot injector valve was worn/unserviceable.

regardless.......bite the bullet and get a properly trained engineer to have a look at it.....it's not worth the risk to screw around with it yourself unless you actualll know what you are doing yourself.

Cheers
FT

[mybrainhurts]

pm99 said:

the pilot light is only supposed to go on when there is flow...it is supposed to start up when you turn the hot tap on...

That doesn't make sense.

The whole point of a pilot light is to fire up the burners when heat is required, so it's always lit.

I go for the thermocouple theory.

If you can see the pilot light, does its flame lick around a metal probe? If so, that's the thermocouple. If it's burnt out, it might feel rough if you can feel it.

[dilbert]

mybrainhurts said:

pm99 said: the pilot light is only supposed to go on when there is flow...it is supposed to start up when you turn the hot tap on... That doesn't make sense. The whole point of a pilot light is to fire up the burners when heat is required, so it's always lit. I go for the thermocouple theory. If you can see the pilot light, does its flame lick around a metal probe? If so, that's the thermocouple. If it's burnt out, it might feel rough if you can feel it.

Unless it has spark ignition. Most modern boilers use a standard spark plug.

[Byff]

If it works ok for the radiators, then I woulds suspect a dodgy zone valve. The boiler will only do one at a time, rads or hot water. The diverter valve is what determins what ssytem is in demand and should kick start the boiler if hot water is required.

Normally, hitting it with a hammer is enouigh, but it should be a universal fitting type if you need to repalce it.

Then agaib, I'm pissed, and my memory isn't what it usewd to be.

>> Edited by Byff on Monday 20th June 07:50