Hi my boiler came up with a F5 fault so I've replaced the overheat stat,thermistors and the pump. But it still keeps blow the overheat stat and coming up with the F5 fault.
The boiler is about 8 years old and up to now has only needed a new diverter valve.
Can anybody help,

On 08/11/2013 18:34, wrote:
Hi my boiler came up with a F5 fault so I've replaced the overheat stat,thermistors and the pump. But it still keeps blow the overheat stat and coming up with the F5 fault.
The boiler is about 8 years old and up to now has only needed a new diverter valve.
Can anybody help,


Does this happen during CH demand or under HW demand or both?

Stephen.

It works fine on the central heating, then when I run the hot water it get too hot and blows the overheat stat

In article ,
writes:
It works fine on the central heating, then when I run the hot water it get too hot and blows the overheat stat

Don't know that boiler, but overheating on hot water is often caused
by a scaled up secondary heat exchanger. If the hot water either isn't
as hot as it used to be at a reasonable flow rate, or the flow rate is
less than it was, that would also point to the same cause.

To descale it, you'll need a lot of descaler (something like Furnox DS-3),
or you could replace it.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 08/11/2013 22:46, Andrew Gabriel wrote:
In article ,
writes:
It works fine on the central heating, then when I run the hot water it get too hot and blows the overheat stat

Don't know that boiler, but overheating on hot water is often caused
by a scaled up secondary heat exchanger. If the hot water either isn't
as hot as it used to be at a reasonable flow rate, or the flow rate is
less than it was, that would also point to the same cause.

To descale it, you'll need a lot of descaler (something like Furnox DS-3),
or you could replace it.


Its a pig of a job to remove the DHW secondary heat exchanger. You have
to remove a short piece of gas pipe within the boiler to get the
secodary heater exchanger out.

You need to descale both sides of the heat exchanger.

ALso there are trwo gauze filters within the boiler ot clean as well

In article ,
Stephen writes:
On 08/11/2013 22:46, Andrew Gabriel wrote:
In article ,
writes:
It works fine on the central heating, then when I run the hot water it get too hot and blows the overheat stat

Don't know that boiler, but overheating on hot water is often caused
by a scaled up secondary heat exchanger. If the hot water either isn't
as hot as it used to be at a reasonable flow rate, or the flow rate is
less than it was, that would also point to the same cause.

To descale it, you'll need a lot of descaler (something like Furnox DS-3),
or you could replace it.


Its a pig of a job to remove the DHW secondary heat exchanger. You have
to remove a short piece of gas pipe within the boiler to get the
secodary heater exchanger out.

You need to descale both sides of the heat exchanger.

The primary side shouldn't scale up - that's only cooling water
down. If the water circulating in the system is dirty, it may block
with rust particles and other debris, but that doesn't dissolve in
descaler very well.

ALso there are trwo gauze filters within the boiler ot clean as well

If those are easier to get at, might be worth trying to cleam just
those to start with, and see if that increases the flow enough.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Thanks for your help Andrew & Stephen. Descaled the heat exchanger and it's working fine now, your right it was a pig of a job, I took the boiler off the wall as I couldn't get it out. I might still replace it while I remember how.
Thanks again

On 09/11/2013 17:21, wrote:
Thanks for your help Andrew & Stephen. Descaled the heat exchanger and it's working fine now, your right it was a pig of a job, I took the boiler off the wall as I couldn't get it out. I might still replace it while I remember how.
Thanks again


that obviously means you had to disconnect the gas supply to the boiler
in order to remove said boiler off the wall.... and then rehang boiler
and reconnect gas....

I presume you're gas safe registered?

The DHW heat exchanger is at the back of the boiler and as mentioned
earlier, you have to remove a short length of gas pipe within the boiler
to get the DHW HE out.

The fact that you could not get the DHW HE out without taking the boiler
off the wall suggests that the hot, cold, feed and return water pipes at
the back were fouling the space needed to manipulate the DHW HE out.

On 09/11/2013 15:06, Andrew Gabriel wrote:
In article ,
Stephen writes:
On 08/11/2013 22:46, Andrew Gabriel wrote:
In article ,
writes:
It works fine on the central heating, then when I run the hot water it get too hot and blows the overheat stat

Don't know that boiler, but overheating on hot water is often caused
by a scaled up secondary heat exchanger. If the hot water either isn't
as hot as it used to be at a reasonable flow rate, or the flow rate is
less than it was, that would also point to the same cause.

To descale it, you'll need a lot of descaler (something like Furnox DS-3),
or you could replace it.


Its a pig of a job to remove the DHW secondary heat exchanger. You have
to remove a short piece of gas pipe within the boiler to get the
secodary heater exchanger out.

You need to descale both sides of the heat exchanger.

The primary side shouldn't scale up - that's only cooling water
down. If the water circulating in the system is dirty, it may block
with rust particles and other debris, but that doesn't dissolve in
descaler very well.



Trouble is that the channels within the DHW HE are tiny. it only takes a
few pieces of magnetitite to block up the channels.

the rads are on 10mm or 15mm or 22mm pipe that is several orders of
magnitude greater than the DHW HE's channels.

ALso there are two gauze filters within the boiler ot clean as well

If those are easier to get at, might be worth trying to cleam just
those to start with, and see if that increases the flow enough.

These two filters a

Cold water inlet filter

and

Return water filter.

They are supposed to protect the DHW HE from clogging up but do not do a
very good job....

In article , Stephen
writes

I presume you're gas safe registered?

If you want to pump that particular fist, provide a citation for the
requirement.

Otherwise don't be a ****.
--
fred
it's a ba-na-na . . . .

On 10/11/2013 12:34, fred wrote:
In article , Stephen
writes

I presume you're gas safe registered?

If you want to pump that particular fist, provide a citation for the
requirement.

Otherwise don't be a ****.

the law says that anyone working on gas appliances must be competent.

It would be very hard for a d-i-yer to defend themselves in court as
competent without some form of paper qualifications if CO or gas leaked
and killed someone.

Moreover, if you are servicing or repairing your own gas appliances the
building insurance would likely refuse to pay for any claim resulting
from a gas appliance fault/defect without evidence of said compentence.

Even people with gas safe certs do make human error type mistakes. That
is is the whole point of professional liability insurance.

I would be prepared to service my own gas appliances if I could
demonstrate my competence to the safisfaction of a court of law or to my
insurance company.

In article , Stephen
writes
On 10/11/2013 12:34, fred wrote:
In article , Stephen
writes

I presume you're gas safe registered?

If you want to pump that particular fist, provide a citation for the
requirement.

Otherwise don't be a ****.

the law says that anyone working on gas appliances must be competent.

Still waiting on that citation for the requirement to be Gas Safe
registered.

Anyway, done to death here so many times it's boring and IIRC last time
was within a month where chapter and verse on the real rules were
provided by better than me. If a future reader wishes to find the real
requirements for working on gas appliances then I'd suggest a trawl back
for that very informative thread.

Thank you and goodnight.
--
fred
it's a ba-na-na . . . .