DHW problems with Eco-hometec combi boiler

[Tim]

Hello,

I'm having some problems with my Eco-hometec combi boiler (EC31S model I believe) and thought I'd ask for advice here before calling them as previous experiences with their service department have not been that positive.

The boiler has been installed for several years now and for most of that time has worked fine. Recently however it has started registering demand for hot water when no taps are on (quite ironic as normally its response to turning on a hot tap is very slow). The problem is usually seen when a hot tap has been turned briefly on and then off again. The normal behaviour, assuming that enough water has been drawn, is that the boiler fires up at this point, runs up to fairly high power and then powers down again. It still does this, but then, a couple of minutes later runs through the whole process again. It repeats this process a variable number of times before eventually settling down.

I can get it to stop doing this by running the hot tap again until the boiler is running and then slowly turning the water off. If I do this then the boiler goes off and stays off.

I've also noticed that it is tending to come on and heat up the internal reservoir of hot water a lot more frequently than it used to and I suspect that it is up to something at night as when I get up some radiators are hot, even though the room thermostat has not been on (and I believe that the system diverts unused hot water into the heating system?). Finally I notice that the first time a hot tap is turned on in the morning the pressure seems very high for a couple of seconds before returning to normal.

I suspected that there was a leak somewhere in the hot water system, but can't find anything obvious. I did find that the valve on the hot water feed to the washing machine was leaking and have replaced this, but to no avail.

So, sorry for the long post, just thought I'd better give as much detail as possible. Can anyone suggest what the problem might be?

Thanks,

Tim.

[Andy Hall]

I have the non-combi version of the MAN Micromat and haven't had problems at all. I do know that until a while ago, Eco Hometec were using self employed fitters around the country to do servicing, but now have their own employees doing the work. Last time I had a service done, it was fine. Another alternative would be to contact MHS Boilers who also distribute the MAN boilers in the UK.

I also have the installation and service manuals for the boiler (including the combi) and the software and lead for a PC to be able to monitor the boiler's behaviour.

On my set up, I have a HW cylinder, the temperature of which is monitored with a remote sensor. This gives better response and control of the HW than using a simple thermostat. If I run the PC software, I can see the temperature of this as well as the boiler flow and return temperatures, the pump speed and the fan speed (which relates to burn rate) and the state of the motorised valves.

All that is by way of introduction.

Looking at the internal schematic for the boiler, it appears that the additional electrical components for the combi version are temperature sensors for the mains cold water and for the mains output hot water. I can't find mention of a flow switch, so as far as I know, the combi part of it works by sensing temperature fall at the internal reservoir rather than directly sensing the flow. There is an internal diverter valve to deliver the primary water to the heat exchanger.

On the non-combi boiler, the HW cycle does not begin until the HW temperature at the cylinder has dropped to about 5 degrees below the set point - i.e. around 55 degrees.

Yes it does, although if it has been on a HW cycle only, then that should be for a very short period of time and is basically to dump heat from the burner heat exchanger. On mine, as the cylinder temperature approaches the set point, the burner is modulated down and so the residual heat is quite small. It could be that on the combi there is a bit more heat to disperse. However, I have never noticed a radiator getting more than slightly tepid when the heating is off which suggests that a lot of cycling is happening.

Based on how I know the non-combi to work, and what I can deduce about the combi from the documentation, there are a few things:

- You could look at the DHW temperature on the main display and see how that is moving around - press the menu button repeatedly to get to this. It may give a clue as to what the controller thinks about the temperature of the reservoir

Beyond this there could be a number of possibilities

- some amount of leak through the HW system. I would expect the pipe from the boiler to be warm then though.

- faulty temperature sensors on the reservoir, or they are not in contact with it properly

- the controller has lost its settings or is faulty

- scaling of the heat exchanger

- faulty diverter valve

To look at the controller parts, you really need the PC software and cable - cost is about £150 for that.

You can buy the spares. The problem is which, and you could end up trying a lot of things before finding the fault.

Economically, I suspect a service call is the best option.

.andy

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[geoff]

In message , Tim writes

A faulty water flow / pressure sensor ?

[geoff]

In message , geoff writes

Having read Andy's post it would seem that it can't be

Too late to look into it now as I'm off to Belgium tomorrow

[Andy Hall]

Geoff, as far as I can see it doesn't have one.

I have the installation manual for mine - non combi version, but has the internal schematic for the combi version as well.

Looking at this, the controller (which is a module with ten or so multiway connectors) has

a) Low voltage sensors

- Primary water flow and return temps,

- (on combi) instantaneous HW flow temp. and cold inlet temp,

- ( on non combi) cylinder stat or cylinder temp sensor

- outside temp sensor

- room temp sensor or Siemens room controller.

b) Safety and fan control

- primary water limit thermostat

- flue temp limit thermostat

- fan speed sensing and drive

c) Mains voltage

- Pump drive and sensing (pump modulates)

- 3way valve (combi)

- Two outputs to drive external pumps or valves depending on selected operating mode.

- Room thermostat if room sensor not used

- gas valve

d) Ignition/Ionisation

e) Controller connection for multiple ganged boilers.

f) Aux. alarm connector for failure

g) RS232 for PC.

I know that the HW on the non combi version (if during a HW timer period) works by using the sensor on the HW cylinder and fires the boiler at 5 degrees below the set point. The same connector on the controller is used for the combi HW temperature sensing.

Therefore as far as I can make out, it's working entirely on detecting the temperature of the HW as there does not seem to be any flow or pressure sensor and no mention of one in the service instructions.

There are about 50 different operating modes which are settable on the controller depending on different factors, so apart from faulty temperature sensors and heat exchanger scaling, I had wondered if the controller could have lost its mode setting. The same controller seems to be used for both combi and non-combi versions. One of the combi temperature sensors is replaced with a shorting plug in the non-combi version and there are a set of operating modes for Combi or non-combi with diverter valve and another for non-combi only with external pump or zone valve to control primary water to the HW cylinder.

.andy

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[geoff]

---------------------------------------------

Off the top of my head, no idea, and I don't know the boiler

If I had time I would look into it, but I'm away until the 14th

Sorry OP, I don't know

[RichardS]

Have fun! Give my regards to the racetrack of lunacy otherwise known as the Antwerp Ring....

-- Richard Sampson

email me at richard at olifant d-ot co do-t uk

[geoff]

In message , RichardS writes

Been there once, I'll be in Liege which is the other end of the country

I have a suit and tie and a new pair of shoes, roll on the wedding !

[IMM]

Maxie that sounds fabulous, I hope you have a great time. Are the shoes spats?

[Simon Stroud]

I have the combi EC31S and have had no problems with it so far - just coming up to its 3rd annual service next month.

Have you noticed any changes in the pattern of temperatures reported on the display when you cycle through them? I've never really got to the bottom of exactly which of the temperatures triggers HW demand. It may be something like a sudden drop in "DHW" temperature reading. It doesn't seem to be the absolute level - mine is quite happy to sit there for long periods of "no demand" and the temperatures can be pretty low - it doesn't then trigger it to fire.

I just did a few experiments just so you can compare with "normal operation".

The boiler had been sitting there for an hour or so with no demand. The readings were: SUP 45, DCW 29, RET 42, DHW 38.

I think DCW is the actual output HW temperature and DHW appears to be somewhere partway along the HW heat exchanger. SUP and RET are presumably flow and return.

So it seems happy to sit there and is making no effort to keep the stored water at anything like my set 55 degrees.

Then I ran a tap for a while until it stabilised: SUP 60, DCW 54, RET 52, DHW 18.

Looks about right - the DHW measurement seems to be some temperature above the mains CW supply, presumably measured part way along the heat exchanger "coil".

Tap off. After it settles into "no demand": SUP 56, DCW 51, RET 57, DHW 17.

It will sit happly like this for a long time and as per the first result the DHW temperature gradually rises and it doesn't fire up.

Just for fun I turned off the boiler at the mains and then ran a hot tap until it was pretty cold. When I switched on it did the deaeration thing then sat without firing at: SUP 28, DCW 17, RET 25, DHW 26.

So it doesn't seem to be the absolute temperature of DHW that triggers firing (although I could have left it a bit longer I suppose to see if it would sit at even lower temperatures).

Then turning on a tap from this condition, just after firing up it said: SUP 30, DCW 20, RET 23, DHW 16.

I am guessing that it detects the SUDDEN drop in DHW measurement to trigger firing, but that's just speculation. Maybe there's some undocumented software setting for how the firing up action works? or maybe you have a duff temperature sensor.

The initial high pressure thing on your boiler HW output is interesting. I've no idea what pressure rise you get on the HW side when it heats the stored water with all taps off. I assume it isn't great because I have a non-return valve (as I have a water softener) so I can't be using the mains supply as an expansion vessel. I'm using either the pipework or the great big fibreglass pressure vessel in the water softener as the expansion vessel I guess. Anyway I haven't had any burst pipes yet. It doesn't sound like you have a leak in the heat exchanger or anything because your boiler pressure gauge would be creeping up all the time and possibly venting. Your high pressure is the other way round, on the mains water side. Strange.

Good luck!

Regards, Simon.

[Andy Hall]

Yes they are. You may also have T numbers representing the sensors, including the outside one.

I think that you may be right. The DCW sensor in the combi replaces the cylinder one on the non-combi, and the DHW one is not present but shorted out. It seems that the naming is round the wrong way somehow.

At any rate, what I notice is that if the cylinder temperature drops slowly from the set 60 degrees because of small drawings of water, nothing happens until 55 degrees is reached. Then the boiler fires but not at full power. However, if I turn on the shower and bath and the temperature falls more rapidly, the boiler is firing up as the temperature is going though about 57 degrees and goes up immediately to full power. I am pretty sure that there is also some logic to prevent the temperature from overshooting by backing of the burn rate as the set point is approached.

The MHS manual is a better translation from German and does document the function number selection as well as the various settings for the operating temperatures and pump and fan operating ranges. There isn't anything explicit in there about specific settings for the combi versions and nothing in the PC software. If anything, it appears that the controller knows that it's a combi because of the presence or absence of one of the sensors. I don't believe that there is even different firmware, because they don't list a different part for the controllers.

.andy

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[Tim]

[...]

Thanks very much for this and for the rest of the suggestions. Thanks to Andy as well for his detailed response - there's quite a lot for me to digest here and I think I also need to do a bit more investigating. In particular I'll run through what the temperature readings are for the various modes of operation.

Having a closer look at all of the hot water taps yesterday showed that there might in fact be a slow leak on the bath hot water tap so I'll have a look at fixing that tonight and see if it helps. Of course, after posting the message yesterday, the boiler behaved almost normally last night, only coming on once when it shouldn't have. I did notice though that the radiators were quite warm when I first got in last night (the thermostat would not have been on) and the hot water pipe leaving the boiler was quite warm for the first few inches or so

- clearly it had been up to something during the day!

If I don't get any joy with looking into these things I'll arrange for Eco-hometec to come out and I'll post the conclusions here.

Thanks again,

Tim.

[IMM]

Maxie, fabulous. Off into the wild blue yonder.

[Andy Hall]

One other thing that I picked up from reading through the manual, is that it says that the boiler stores 10 litres of *primary* water in the HW heat exchanger circuit and maintains that at the set point of the DHW. If the temperature sensor is monitoring that, then it would be an explanation of the boiler firing after some long period of time if you have a slow leak at a tap.

If you can get to the boiler when one of these phantom cycles happens, I would expect that it does not dump heat from the burner heat exchanger into the CH circuit until after the burner has gone off. This is how mine behaves at the end of a cycle of reheating the cylinder and it does it by opening the CH zone valve briefly with the pump running. I would expect a similar thing to happen with the combi except tha tthe diverter valve would switch over to the CH circuit. If the CH flow pipe is feeling warm *during* the cycle and before the burner goes off, then this may mean a faulty diverter valve. This is another check that you can make pretty easily.

Another one to try, is after a HW cycle, turn on a hot tap very slowly

- literally a drip or slow trickle and see how much water you collect before the boiler fires again. This will give you another clue about the leak through tap theory in that if it's only a few litres, it's plausible.

.andy

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[IMM]

The leak would explain a lot. This is the first line of attack, get that sorted and see what happens. The rad circuit being warm may be that it is dumping heat. Some combi's do this. It may be that the CH clock was on and the stat called for heat. Last night my system cut in as it has been chilly at times over the past 3 days.

[Tim]

It's looking like this may be the problem. I managed to catch the boiler as it started one of these cycles. I grabbed both of the output pipes and found that though the display read "DHW Demand", nothing was happening to the hot water pipe, only the CH pipe warmed up (quite considerably).

Cheers,

Tim.

[Tim]

[...]

Thanks to everyone for the advice and suggestions. An engineer came out from Eco-hometec yesterday and immediately diagnosed the problem as a faulty actuator rather than the divertor valve itself. Fixed in 5 minutes and no call-out charge as the boiler had been serviced fairly recently - just had to pay for the new part.

It seems that the company has changed considerably since I last had to deal with them in any serious way as this time they were efficient, friendly and quick and the engineer was excellent. If I'd known that I'd have contacted them immediately and probably saved you all the trouble of trying to diagnose the problem remotely!

All the best,

Tim.

[Andy Hall]

Not a bad deduction though......

I'm glad it's fixed.

.andy

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[Tim]

Absolutely - it was spot on and allowed me to sound like I knew what I was talking about when discussing it with the engineer on the phone.

Me too!

Cheers,

Tim.