DHW problem with Vaillant Ecomax 824E

[robisoft]

I would be greatful for any help/advice anyone can offer please.

I have a Vaillant Ecomax 824E combi. It was installed in November 1999 and was fine for the first 5 years or so. The system was treated with Fernox from day one which I kept topped up. We started to have DHW problems with large temperature swings and various faults (F23 - water flow restricted - was common) . My solution was to take out the DHW heat exchanger and flush it with mains water. I would also flush the main heat exchanger in a similar way. I used to dislodge plenty of debris but this has reduced of late. I also had the whole system power flushed (but this did not include the boiler itself) and treated the system with Sentinel. We continued to have problems which I could temporarily alleviate by flushing the heat exchangers until finally the boiler would not even run on CH for very long.

I have now replaced both heat exchangers, simulateously flushing the system and retreating with Sentinel. CH is now perfect and the fault messages have ceased. However the DHW is nowhere near as hot as it once was at the shower. The boiler gets up to about 68 degrees, the gas reduces until it is down to 60 and modulates between the two. (On CH it gets up to 80.) I am confident the pump and diverter valve are OK. So do I have a PCB problem do you think? The waterways must all be clear now so I am at a bit of a loss. I can get a hot bath by slowly filling it. It is almost as if the boiler cannot cope with the demands of the shower yet it used to and the CH is very hot.

A couple of other points. The water mains pressure is very good. I noted that the new DHW heat exchanger came with a couple of tubes which fitted into the DHW inlet and outlet - the old one did not have them but nevertheless I fitted them.

Thank you for reading this - your collective experience is far greater than mine and I am reluctant to buy a new PCB on a whim.

[Andy]

Not entirely sure I understand you here. I have a Vaillant Turbomax. It will get the DHW up to a maximum of 63-64 degrees, which is correct - any more might lead to scalding. The CH water can be set up to 82 degrees ( 89 is another option available, on the Turbomax anyway ). I fail to see that your combi is therefore doing anything wrong. Remember it is winter, the rising main temperature may be only 5C, and thus the DHW loop will be unable to raise the water temperature to the level it can in summer/autumn ( at maximum flow ). I cannot run my shower flat out in winter on my 828 Turbomax and get the full shower temperature range, but I turn it down a little and that solves the problem.

Andy.

[gasman pete]

firstly what is the flow rate that you are testing the boiler at? what tempreture differential are you getting at the tap? what gas rate is the boiler burning in domestic water mode? pete

[robisoft]

Thanks Andy for taking the trouble to respond.

When I mentioned that the boiler modulates between 60 and 68 degrees, I was referring to the displayed temperature which is that coming out of the main heat exchanger - not that at the tap (which I agree should be limited to 60 or so). So this is the temperature of the water going into the DHW exchanger. I accept all your points but I know that in the past it has achieved better than this - I was expecting the displayed temperature to get into the 70s.

With your boiler what is the displayed temperature range on DHW flat out?

[robisoft]

Thanks Gasman Pete for taking the trouble to respond. I would have difficulty answering your questions in detail although I may have to figure out how to measure these parameters if I have to prove whether the boiler is achieving its rated performance or not. All I can offer is that in the past it performed better than this.

[gasman pete]

you can do a simple test if you let me know what type of gas meter you have... and what colour. it will tell you under the dial

pete

[robisoft]

Hi gasman pete!

My gas meter is beige and appears to be a Schlumberger R5. Does this give you enough to tell me how to do a simple test? Thanks.