Boiler working but not firing to heat shower water

Elki · 26 Feb 2004

Hi Guys...hoping you can help me.

My combi boiler works fine - EXCEPT when I turn on my shower or bathroom sink tap it doesn't fire up. At the moment to avoid cold showers I turn on the kitchen sink to get the boiler fired up, then turn on the shower, then turn off the kitchen sink - a palava in the mornings! The heating is working fine.

It's happens mostly in the mornings, when the water is shared between the flats in my building. The pressure guage on the boiler is at 0.5 and I'm on the first floor. Could this be too low?

I could call in a serviceman, but as the boiler is mostly working, I'm thinking it could be simple and something I could fix...?

Your advice greatly appreciated!

ollski · 26 Feb 2004

not much details but I don't know a combi that works properly on 0.5bar. Check the manual but I would guess at least 1 bar cold.

CH4 · 26 Feb 2004

Elki,

Clearly, the water flow rate through the boiler, to your bathroom, is too low to operate the boiler's domestic hot water flow switch. In the morning, time how long it takes to fill a measuring jug (or bottle of known volume) from a hot tap in your bathroom. Work out the flow rate in litres per minute, and compare it to the minimum value specified in the manufacturer's instructions.

If the flow rate is above the boiler's minimum, then the flow switch needs to be repaired/replaced. Otherwise, the mains water pressure may be too low to supply your bathroom at a flow rate above the minimum, or there could be a constriction in the pipework - somewhere between your boiler and bathroom.

The 0.5 mbar on your boiler's pressure gauge is the pressure of the central heating water. This pressure seems a little low, but check what it should be in the manufacturer's instructions. You may need to add more water to the system via the filling loop.

Elki · 27 Feb 2004

Thanks CH4 - what you say sounds right although I'm not that familiar with some of the terms. If it's the guage is something I can alter myself, as I've had someone in to do this before? There are two 'taps' for hot and cold and I believe I can open these up a bit more - does this sounds right?

Would you mind explaining where the filling loop is?

Would it have anything to do with the water pressure coming into the building - where the stopcock is?

Thanks guys.

boilerbeasty · 27 Feb 2004

Normally the boiler will just have simple open/close taps for the central heating and the cold(in),hot(out) pipes, and one for the gas. These aren't normally adjustable.

However, the incoming cold water stopcock might not be fully open. This may be a brass tap under your kitchen sink - have a look around. If you can't find one, go outside and close everyone else's stopcocks so you get a good flow in the morning (joking).

Has it always been like this ? Perhaps the overall pressure to your building has dropped ? Any plumbers got a view about this ?

Elki · 27 Feb 2004

I think it may be the overall water pressure as two previously empty flats have now been filled demand for water has inceased. They might have adjusted my external stop cock by mistake? I'd be interested to hear what any plumbers have to say.
Thanks

waran · 27 Feb 2004

Elki,

I'm not a plumber but my girlfriend occasionally has a similar problem with her combi.

As I understand it you may need to add more water to the system to increase the pressure within the circuit. On the pressure guage there is often an indicator that tells you how much pressure is needed (on her system it's a red marker). If the pressure guage (her's is a white hand) is below this then you need to add some water to the system. There should be a little valve under the boiler which needs to be turned to allow more water in. (I don't think it'll be as big as the taps you describe - they sound like they are the main input output taps) As you turn it you'll hear water enter and the pressure will creep up. Wait until it's above the red mark (or whatever you have ) and then close it again.

Otherwise the problem might have something to do with the divertor valve but that will need a plumber to sort out.

Hope it helps

boilerbeasty · 27 Feb 2004

The CH circuit pressure is not related to the mains cold water (and HW flow) pressure problem. But an earlier poster pointed out that 0.5bar is low for the CH pressure and ought to be increased a little, and as waran says its fairly simple to do.
I'd be fairly sure its the DHW flow switch, as previously mentioned. Its probably not broken, just not getting the flow from the mains now you have new neighbours.

Elki · 27 Feb 2004

Thanks guys, I'll have a look for the valve tonight. It's an old Alpha Ocean combi, so if anyone has any hints as to where I'll find the valve I'd be gratfeful.
Thanks again,
elki

DP · 27 Feb 2004

The boiler uses (if I am not mistaken) a sunt diverter valve. The unit does not look like a normal valve (it has 5 pipes connected to it). It is highly unlikely Elki will be able to carry out repairs on the valve ( based on not knowing what the valve looks like). Boiler does not have a flow switch commonly found on the Worcester or Ferrollis.

The diverter has a top section (manifold) which houses a diaphragm. Under normal cirumstances the water on both sides of the diaphragm is at equal pressure. When a hot tap is run, pressure above the diaphragm decreases causing the diverter section to shift from CH mode to HW mode. At the same time, a spindle (connected to diaphram gubbins) operates a switch that tells the boiler to get cracking as there is a HW demand in place (burner goes to maximum rate)

Elki I suspect there is a hole in the diaphragm. Only when you run two taps is the pressure above the diaphragm low enough to operate the switch. The hole will get bigger. I suspect the water is not as hot.

Elki · 4 Mar 2004

I had someone round and they thought it was the divertor valve, but they quoted me such an extortionate rate that I've decided to join the British gas scheme - whereby they fix it before you go on their care scheme.

Do you think that this problem can be fixed on their first visit?

Thanks, elki

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Boiler working but not firing to heat shower water

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