Heating/oil boiler problem

virtual_john

Hi All,

I am having a strange issue with my heating system.

Some specifics first:
Firebird heatpac S 70 boiler, Controlled by Horstmann H37XL Channelplus Electronic Central Heating Programmer Series 2. We have 2 x thermostats, 1 upstairs, and 1 downstairs.

When all 3 channels on the Horstmann are set to off, the boiler still fires up, the only way to turn it off is via the switch on the wall (the one with the fuse in it) for the heating.

So I called my friend out who is a good plumber and has done courses on boilers etc...

He spotted some wires inside the boiler that had been chewed on by mice, so we fixed that by cutting away the bits that were chewed on - luckily the cables were long enough. So we thought that it was shorting out, causing the boiler to fire.

So, we thought it was fixed, and it was working well for 6 days, the boiler fired a few times when nothing was on but was still working... it fired during the night too (but the temp was not low enough in the house to trigger the stat)... then I got home today to light the fire and stick the heating... heating came on grand downstairs only, because the stat upstairs was set to 13/14 degrees for night time... let it fire for about 15 mins until I got the fire going, turned it off and headed to the shop. Then got home, turned the heat on upstairs, with the stat now turned up, and nothing - the boiler wasn't firing up at all. Noticed the yard was wet (it hadn't been raining), so that water came from the overflow pipe from the attic. Then I did a reset on the thermostat within the boiler itself... which worked after it cooled down a bit.

So the boiler firing by itself is causing the boiler to overheat??? And need a reset?
I can hear the valves closing when I turn the different channels off - so they seem to be working fine.

So, now we are turning the heating off at the switch to stop the boiler overheating and just turning it on when we need it - luckily it has not been a cold winter so far.

Since then I have replaced the horstmann control until in the kitchen. Still have the same issue though.

So, I am thinking that maybe the problem is the thermostat within the boiler itself is at fault?
There does not seem to be a frost stat in there from what I can see - just an imit dual stat.

Does anyone have any suggestions?
Or has anyone seen or dealt with an issue like this before?

Thanks in advance, John.

K.Flyer

It sounds like you have a faulty zone valve and that one of them is still providing a switched live to the boiler, even when in the off position.
Either that or your mice have done further damage elsewhere.

virtual_john

Thanks K.Flyer...

I have checked all of the cables and wires and they look fine... I will check them again though just in case - maybe there is damage done where I can't see too though!

Is there a way that I can rule out the zone valves, one by one, without replacing them?

Thanks, John.

Dtp1979

virtual_john wrote: »

Thanks K.Flyer...

I have checked all of the cables and wires and they look fine... I will check them again though just in case - maybe there is damage done where I can't see too though!

Is there a way that I can rule out the zone valves, one by one, without replacing them?

Thanks, John.

What type of zone valves have you got? Some can be unplugged. If you unplug one at a time then that'll show up the faulty one

virtual_john

>>>>What type of zone valves have you got? Some can be unplugged. If you unplug one at a time then that'll show up the faulty one


I don't know off the top of my head, but I'll check them out tonight and report back!

Thanks again, John.

virtual_john

Hi,

So I have 2 x Danfoss HPA2 and 1 x Myson MPE222.

Does anyone know if these actuator models are interchangeable?
If I buy a new Danfoss for testing, will that also be able to replace the Myson if that turns out to be the faulty one?

I have left the system turned on for now to see if the problem happens again in a few days or whatever - or if I notice anything before it happens.

I thought though that if it was a faulty actuator that the problem would be there 100% of the time?
Unless the hot water one is faulty as we only use that once or twice a week, and maybe that triggers the problem?

Thanks a million, John.

Dtp1979

virtual_john wrote: »

Hi,

So I have 2 x Danfoss HPA2 and 1 x Myson MPE222.

Does anyone know if these actuator models are interchangeable?
If I buy a new Danfoss for testing, will that also be able to replace the Myson if that turns out to be the faulty one?

I have left the system turned on for now to see if the problem happens again in a few days or whatever - or if I notice anything before it happens.

I thought though that if it was a faulty actuator that the problem would be there 100% of the time?
Unless the hot water one is faulty as we only use that once or twice a week, and maybe that triggers the problem?

Thanks a million, John.

Not always the case. Sometimes the fault can only happen occasionally.

virtual_john

Thanks Dtp1979!

I suspect the hot water actuator might be guilty then... i guess i'll start there.

Thanks, John.

Dtp1979

virtual_john wrote: »

Thanks Dtp1979!

I suspect the hot water actuator might be guilty then... i guess i'll start there.

Thanks, John.

Be careful because there's a permenant live going to each valve irreguardless of whether the boiler is on or not

virtual_john

>>>>Be careful because there's a permenant live going to each valve irreguardless of whether the boiler is on or not

Yep - thanks... I'll have everything off at the main trip switch.

Thanks, John.

RJF

check circulating pump

K.Flyer

RJF wrote: »

check circulating pump

How would a circulating pump cause the boiler to fire up by itself?

RJF

It wouldn't. However if the overheat stat is tripping when it does fire then this could mean circ pump is struggling. On reflection this may also be that there is no bypass circuit when both valves are closed.

virtual_john

>>>>> It wouldn't. However if the overheat stat is tripping when it does fire then this could mean circ pump is struggling. On reflection this may also be that there is no bypass circuit when both valves are closed.

The pump itself seems to be fine, from what I can see. My friend checked it out also and said that it was working fine.
It is quite possible that there is no bypass circuit!

One thing I noticed is that if I set the hot water motorised valve to manual, the boiler will fire all of the time - is that expected?

Thanks, John.

John T Carroll

virtual_john wrote: »

>>>>> It wouldn't. However if the overheat stat is tripping when it does fire then this could mean circ pump is struggling. On reflection this may also be that there is no bypass circuit when both valves are closed.

The pump itself seems to be fine, from what I can see. My friend checked it out also and said that it was working fine.
It is quite possible that there is no bypass circuit!

One thing I noticed is that if I set the hot water motorised valve to manual, the boiler will fire all of the time - is that expected?

Thanks, John.

If the overheat stat is tripping and there isnt a problem with the circ pump or you havnt a mice caused problem then its quite possible that the problem lies with the hot water motorised valve, the valve may be almost closing fully but the limit switch for supplying power to the boiler/circ pump isnt opening, there would then be no circulation through the boiler and it would trip out the overheat stat. A neighbour of mine had that problem with the hot water motorised valve (myson MPE222) and that was his problem, symptoms were very like yours. When these valves are de eneregised, a spring in the valve head returns the valve to the closed position and opens the switch that supplies power to the boiler/circ pump, this spring had gone faulty in my neighbours and wasnt closing the valve sufficiently to open the power switch but the valve itself was almost fully closed, sometimes the valve itself can become "sticky", a bit unusual maybe but can easily be checked by removing the head from the motorised valve, your plumber (or maybe yourself, if competent) can easily check out these relatively simple things.
Re your query re the hot water motorised valve, if you are referring to opening it with the manual lever then yes it will close the switch supplying power to the boiler which will fire up and cut in/cut out on its own thermostat as per normal assuming the boiler main switch is on.

Also just check that someone hasnt turned up the Boiler thermostat fully as the Firebird will trip on the overheat stat even if everything is working normally, there is normally no bypass circuit to my knowledge.

virtual_john

Thanks very much John T Carroll!!

John.

virtual_john

Thanks John T Carroll - good clear explanation.