Low hot water pressure

[TrueBlue]

I've got a Vokera Compact combi and I've got a problem with it. The heating for the rads works fine but the hot water pressure is terrible. Downstairs in the kitchen the hotwater comes out at a trickle, but upstairs in the bathroom it is virtually non existence. When I first turn on a hot water tap there is a burst of water for a few seconds then it dies down. Also, the boiler doesn't kick in right away and takes a few minutes to heat the water. It's almost as if the boiler doesn't know I'm calling for hot water. The cold water pressure in the house is immense and I've made sure the cold water inlet valve to the combe is fully open.

Any ideas what the problem is?

 

[chrishutt]

Could be a diaphragm or flow switch problem (don't know off hand which the Vokera has).

 

[TrueBlue]

There is an actuator just after the inlet valve, could it be anything to do with that? Daiphram? Flowswitch? what parts are they? (see pic)

 

[TrueBlue]

The inlet valve I opened was item 30 and the actuator I'm on about is item 26.

 

[chrishutt]

Item 26 looks like a flow switch to me, but as I said i don't know this boiler. Can you test if the electrical switch on it operates in response to flow?

Actually, thinking about it a bity more, something's retricting the flow. Could there be a blocked filter on the cold inlet?

 

[TrueBlue]

item 26 is listed as an actuator, which I suppose could be called a flow switch too. I'll check that later. Where would the filter be if there was one? Can it be seen on that diagram?

 

[TrueBlue]

Item 26 looks like a flow switch to me, but as I said i don't know this boiler. Can you test if the electrical switch on it operates in response to flow?

The flow switch doesn't operate when I turn on my tap. I believe the flow switch is designed to operate at a flow rate of 2l/min, but I only appear to have a flow rate of 1.8 l/min so the flow switch is never going to operate. i can't understand what is restricting the flow because the cold water pressure is great.

 

[chrishutt]

Has the hot water flow suddenly decreased, or has it decreased slowly over time?

If it's sudden, I would be looking for some component in the boiler (such as a flow restrictor?) that might have failed. If slow, it might be scaling up of heat exchanger (has you water been exceptionally hot in the past?).

Unfortunately the picture of your manual is not very clear and the new Vokera web site is not on-line for 2 weeks. Can anyone supply a pdf manual for this boiler?

 

[TrueBlue]

It has been getting worse over time. You think it could be scaling then? I'm surprised that scaling could affect the pressure so much. The hot water as I say, is 1.8 liters per minute and I just tested the cold water pressure at 1 liter per SECOND

 

[TrueBlue]

How would I go about removing the scaling.

 

[chrishutt]

I just tested the cold water pressure at 1 liter per SECOND

That's not a measurement of pressure. It's flow rate, which is different but related. It's exceptionally high at 60 litres/min! Is that from just one tap?

You should be getting around 10 litres/minute of hot water from a combi, depending on power output, so your clearly suffering some major flow restriction.

You appear to have a combined primary and secondary heat exchanger (sometimes called double pass?). These may be more prone to scaling up, and could be very expensive to replace. Descaling should be possible but might require dangerous chemicals and can't be recommended as DIY project.

 

[TrueBlue]

The boiler is 10000 BTu from memory and it is only about 18 months old, so it shouldn't be that bad, should it?

 

[chrishutt]

Depending on how the boiler works, a fault could possibly cause quite rapid scaling. Nevertheless you wouldn't expect anything like that in 18 months. If it's so new, why aren't you getting on to the installer?

 

[TrueBlue]

It's out of warranty I'm afraid. I don't think it's an installation problem, though I will ask the installer to have a look at it. Trying to get a time which suits us both is a little difficult though.

 

[sabwood]

I've got a Vokera Compact combi and I've got a problem with it. The heating for the rads works fine but the hot water pressure is terrible. Downstairs in the kitchen the hotwater comes out at a trickle, but upstairs in the bathroom it is virtually non existence. When I first turn on a hot water tap there is a burst of water for a few seconds then it dies down. Also, the boiler doesn't kick in right away and takes a few minutes to heat the water. It's almost as if the boiler doesn't know I'm calling for hot water. The cold water pressure in the house is immense and I've made sure the cold water inlet valve to the combe is fully open.

Any ideas what the problem is?[/quote

Hi True Blue. I have the same problem with my Vokera Boiler. I think the filters might need cleaning out. Did you get yours fixed and what was the problem ?