Thanks again John (and others),

That one you posted the photo of looks almost identical to mine.

So, I've taken out the temperature sensors on both the DHW pipe and the heat exchanger. Both give about 11K Ohms at cold and that drops pretty quickly to 500 Ohms or less when I get the hairdryer on them.

Makes me think that they might be functioning ok, though I don't have any data on what the actual readings should be. The fact that both exhibit the same characteristics makes me think they are not kaput.

So I'm struggling now. There does seem to be some corrosion around the diverter valve (I shall try to post a photo(s)) but it is dry as a bone there now.

Anything suggested I can try?

Thanks a million again for helping.

Photos showing the slight corrosion (looks historic) should be he https://1drv.ms/f/s!AviGTSqlox7cipQYjLFVW6iS0ErJbg

On 16/10/2018 02:36, wrote:

So I'm struggling now. There does seem to be some corrosion around the diverter valve (I shall try to post a photo(s)) but it is dry as a bone there now.

Anything suggested I can try?

Thanks a million again for helping.

Photos showing the slight corrosion (looks historic) should be he https://1drv.ms/f/s!AviGTSqlox7cipQYjLFVW6iS0ErJbg

How much is a new diverter valve?
It's going to pack-up sooner or later you can be sure of that. Switch it
out, if it solves the problem you're sorted, if it doesn't well, you've
got a spare to switch out in the future when it does pack-up.


Think about it,
The symptoms have got possessively worse as the diverter valve has been
gradually seizing up and opening less as the weeks go by so boiler is
shutting down quicker as generated heat can't be dumped to DHW quickly
enough. And my own one EcoTec boiler diverter valve packed up within
the initial warranty period and failed again about 5 years later.

Can't see a pressure sensor etc gradually failing, it would either work
or not work (would be my guess)

On 16/10/2018 02:36, wrote:
Thanks again John (and others),

That one you posted the photo of looks almost identical to mine.

So, I've taken out the temperature sensors on both the DHW pipe and
the heat exchanger. Both give about 11K Ohms at cold and that drops
pretty quickly to 500 Ohms or less when I get the hairdryer on them.

Well that sounds like the expected behaviour for a NTC thermistor. The
manual may have expected values.

Makes me think that they might be functioning ok, though I don't have
any data on what the actual readings should be. The fact that both
exhibit the same characteristics makes me think they are not kaput.

Yup, that sounds plausible to me.

So I'm struggling now. There does seem to be some corrosion around
the diverter valve (I shall try to post a photo(s)) but it is dry as
a bone there now.

It looks like something has leaked a fair bit, and its in the area of
the valve.

Anything suggested I can try?

Looking at the symptom you described, (i.e. hot water then going cold,
and the lockout code for an overheat detection), it could be you have an
obstruction in the primary side of the DHW HX. If you were getting
inadequate flow through that, that could explain both the loss of
temperature on the DHW, and possibly a higher than expected temperature
rise on the primary side since there would be too lower a rate of heat
flow to the DHW.

Hence it might be worth taking out the plate heat exchanger, and
checking you can flush through its primary side in both directions... (I
am guessing the secondary side is ok if you get an adequate flow rate of
hot water (even if its not hot!)



Thanks a million again for helping.

Photos showing the slight corrosion (looks historic) should be he
https://1drv.ms/f/s!AviGTSqlox7cipQYjLFVW6iS0ErJbg



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Tuesday, October 16, 2018 at 9:16:12 AM UTC+1, www.GymRatZ.co.uk wrote:
On 16/10/2018 02:36, wrote:

So I'm struggling now. There does seem to be some corrosion around the diverter valve (I shall try to post a photo(s)) but it is dry as a bone there now.

Anything suggested I can try?

Thanks a million again for helping.

Photos showing the slight corrosion (looks historic) should be he https://1drv.ms/f/s!AviGTSqlox7cipQYjLFVW6iS0ErJbg

How much is a new diverter valve?
It's going to pack-up sooner or later you can be sure of that. Switch it
out, if it solves the problem you're sorted, if it doesn't well, you've
got a spare to switch out in the future when it does pack-up.


Think about it,
The symptoms have got possessively worse as the diverter valve has been
gradually seizing up and opening less as the weeks go by so boiler is
shutting down quicker as generated heat can't be dumped to DHW quickly
enough. And my own one EcoTec boiler diverter valve packed up within
the initial warranty period and failed again about 5 years later.

Can't see a pressure sensor etc gradually failing, it would either work
or not work (would be my guess)

Thank you. That's good advice.

I was just hoping there might be some way to determine the diverter valve BEFORE buying a new one. Just me being tight I guess, but it's always nice to know something is actually broken first.

Thanks.

On Tuesday, October 16, 2018 at 11:47:57 AM UTC+1, John Rumm wrote:
On 16/10/2018 02:36, wrote:
Thanks again John (and others),

That one you posted the photo of looks almost identical to mine.

So, I've taken out the temperature sensors on both the DHW pipe and
the heat exchanger. Both give about 11K Ohms at cold and that drops
pretty quickly to 500 Ohms or less when I get the hairdryer on them.

Well that sounds like the expected behaviour for a NTC thermistor. The
manual may have expected values.

Makes me think that they might be functioning ok, though I don't have
any data on what the actual readings should be. The fact that both
exhibit the same characteristics makes me think they are not kaput.

Yup, that sounds plausible to me.

So I'm struggling now. There does seem to be some corrosion around
the diverter valve (I shall try to post a photo(s)) but it is dry as
a bone there now.

It looks like something has leaked a fair bit, and its in the area of
the valve.

Anything suggested I can try?

Looking at the symptom you described, (i.e. hot water then going cold,
and the lockout code for an overheat detection), it could be you have an
obstruction in the primary side of the DHW HX. If you were getting
inadequate flow through that, that could explain both the loss of
temperature on the DHW, and possibly a higher than expected temperature
rise on the primary side since there would be too lower a rate of heat
flow to the DHW.

Hence it might be worth taking out the plate heat exchanger, and
checking you can flush through its primary side in both directions... (I
am guessing the secondary side is ok if you get an adequate flow rate of
hot water (even if its not hot!)



Thanks a million again for helping.

Photos showing the slight corrosion (looks historic) should be he
https://1drv.ms/f/s!AviGTSqlox7cipQYjLFVW6iS0ErJbg



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Thanks again John,

What you describe could indeed be the case. It might also explain why the analogue pressure gauge is sitting with a static reading, even when drained down on the CH. Could be just blocked pipe.

The heat exchanger does get hot but I am not sure how quickly it should happen. It would make sense therefore that it is either the HX itself (blocked) or the diverter valve which isn't diverting fully.

Maybe time to call a Vaillant engineer!

Cheers

On 16/10/2018 14:56, wrote:

Thanks again John,

What you describe could indeed be the case. It might also explain why the analogue pressure gauge is sitting with a static reading, even when drained down on the CH. Could be just blocked pipe.

The heat exchanger does get hot but I am not sure how quickly it should happen. It would make sense therefore that it is either the HX itself (blocked) or the diverter valve which isn't diverting fully.

Maybe time to call a Vaillant engineer!

Valliant will give you the option of £299 engineer fix including parts
except for Heat exchanger or for the same price yo buy a D&G boiler
insurance that lasts 6 months and includes all parts INCLUDING heat
exchanger(s).

Dunno about the Valiant diverter valves but on my home MAN boiler I can
remove the actuator head and when the hot tap is run the plunger pin
comes out of the head to operate the valve. I can also manually operate
the valve pin with a "prodder" which then checks operation of the
valve it's self.
What used to happen on that one was the water seal around the valve
plunger would weep and C/H water would get into the actuator head
causing things to corode and jam. Replaced the head twice and last year
the weep became a full on leak so replaced both the diverter valve body
and actuator head at some extortionate price but it had been re-designed
so hopefully it will be more reliable than the original.

On 16/10/2018 14:56, wrote:
On Tuesday, October 16, 2018 at 11:47:57 AM UTC+1, John Rumm wrote:
On 16/10/2018 02:36, wrote:
Thanks again John (and others),

That one you posted the photo of looks almost identical to mine.

So, I've taken out the temperature sensors on both the DHW pipe
and the heat exchanger. Both give about 11K Ohms at cold and
that drops pretty quickly to 500 Ohms or less when I get the
hairdryer on them.

Well that sounds like the expected behaviour for a NTC thermistor.
The manual may have expected values.

Makes me think that they might be functioning ok, though I don't
have any data on what the actual readings should be. The fact
that both exhibit the same characteristics makes me think they
are not kaput.

Yup, that sounds plausible to me.

So I'm struggling now. There does seem to be some corrosion
around the diverter valve (I shall try to post a photo(s)) but it
is dry as a bone there now.

It looks like something has leaked a fair bit, and its in the area
of the valve.

Anything suggested I can try?

Looking at the symptom you described, (i.e. hot water then going
cold, and the lockout code for an overheat detection), it could be
you have an obstruction in the primary side of the DHW HX. If you
were getting inadequate flow through that, that could explain both
the loss of temperature on the DHW, and possibly a higher than
expected temperature rise on the primary side since there would be
too lower a rate of heat flow to the DHW.

Hence it might be worth taking out the plate heat exchanger, and
checking you can flush through its primary side in both
directions... (I am guessing the secondary side is ok if you get an
adequate flow rate of hot water (even if its not hot!)



Thanks a million again for helping.

Photos showing the slight corrosion (looks historic) should be
he https://1drv.ms/f/s!AviGTSqlox7cipQYjLFVW6iS0ErJbg


Thanks again John,

What you describe could indeed be the case. It might also explain
why the analogue pressure gauge is sitting with a static reading,
even when drained down on the CH. Could be just blocked pipe.

Well to be fair, those small pressure gauges quite often go tits up
anyway, so I would not read too much into that.

The heat exchanger does get hot but I am not sure how quickly it
should happen. It would make sense therefore that it is either the
HX itself (blocked) or the diverter valve which isn't diverting
fully.

If the diverter did not divert fully, then you would expect to bleed
heat into the rads when calling for DHW - so they would get warm, the
DHW would be cooler than expected, but you would be unlikely to get an
overheat situation, since you would have adequate heat sinks.

Maybe time to call a Vaillant engineer!

Cheers



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/