Variable Hot Water - Vokera Excell 80 SP

[thisbee81]

I have an issue whereby when in the shower, the hot water varies in temperature. Every few minutes the heat drops for a minute or so and then comes back.

Just had the boiler serviced and the engineer said that the issue was sludge in the heating system. This was causing a blocking in the heat exchanger (the central heating one?) and because the water wasn't getting through the whole system (presumably the bit in the boiler before it is routed to water or heating?) temperature was building and the burner was cutting out.

He suggested a power flush and replacement of the heat exchanger. I wanted to know if it is the central heating exchanger that needs replacing? Presumably, as that one is the one blocked - although it is the hot water that is being affected.
Any advice gratefully received.

 

[Agile]

Can you try the shower while you run a basin hot tap with about half flow?

Does the hot tap also go cold like the shower?

Tony

 

[thisbee81]

Can you try the shower while you run a basin hot tap with about half flow?

Does the hot tap also go cold like the shower?

Tony

Yes - it affects all the hot water. Just more noticeable in the shower.

 

[ianmcd]

Does your heating work OK ?

 

[Agile]

Turn on a hot tap and SLOWLY increase the flow rate until the boiler fires and leave it at that flow setting.

Measure that flow rate in litres per minute!

Tony

 

[thisbee81]

Turn on a hot tap and SLOWLY increase the flow rate until the boiler fires and leave it at that flow setting.

Measure that flow rate in litres per minute!

Tony

Thanks Tony - I'll try that. What am I looking for?

 

[thisbee81]

Does your heating work OK ?

Yes - heating working fine. Bled the radiators recently and everything seems fine.

 

[ianmcd]

I would be more inclined to look at the DHW plate heat exchanger than the main heat exchanger , your engineer however has been in front of the boiler and has run his tests, so I would never second guess another engineer that has actually seen the boiler

 

[thisbee81]

I would be more inclined to look at the DHW plate heat exchanger than the main heat exchanger , your engineer however has been in front of the boiler and has run his tests, so I would never second guess another engineer that has actually seen the boiler

Fair enough - my question is that I can't remember which exchanger he was talking about replacing. If it is the central heating that is suffering with sludge, I assumed it must be the central heating exchanger that was blocked and acting up, which was having a knock on for the hot water. But I'm not sure.

Basically, once I've had a powerflush, I was going to get one of the exchangers replaced - but not sure which one.

 

[Agile]

Turn on a hot tap and SLOWLY increase the flow rate until the boiler fires and leave it at that flow setting.

Measure that flow rate in litres per minute!

Tony

 

[ianmcd]

I would be more inclined to look at the DHW plate heat exchanger than the main heat exchanger , your engineer however has been in front of the boiler and has run his tests, so I would never second guess another engineer that has actually seen the boiler

Fair enough - my question is that I can't remember which exchanger he was talking about replacing. If it is the central heating that is suffering with sludge, I assumed it must be the central heating exchanger that was blocked and acting up, which was having a knock on for the hot water. But I'm not sure.

Basically, once I've had a powerflush, I was going to get one of the exchangers replaced - but not sure which one.

I wouldnt be getting a powerflush done to be honest, they are expensive and dont really work, you would be better with a chemical flush if needed and a return filter installed, I have never changed a main heat exchanger on one of these for your symptoms but have changed a few plate heat exchangers