Baxi 35/60 Intermittent Failure

lansing

Hi, I am having a very annoying intermittent failure with my Baxi 35/60.

During last summer I was having a few intermittent failures, occuring maybe 1 in 20 times I'd turn run the "hot water" boiler. Sometimes it would not turn on from cold and other times it would not kick back in after it cooled down. It always had the same failure. The 60 degree light would flash indicating a low pressure / pump fault within the boiler. A power reset would get the boiler going again.

My plumber tried changing the diaphragm, thinking it was sticking but that didn't work. He eventually changed the PCB and it all worked perfectly for about 2 months.

However now the problem is back again and is much more frequent. If I turn on "radiators" in the house and then switch them off and then try to turn on "hot water" the 60 degree light will flash every single time. A power reset will not get it going anymore. Instead I have to turn on the "radiators", to get the boiler going then turn on "hot water" in parallel and once I know that's kicked in I can turn off the "radiators" and the "hot water" will continue to work. However when the hot water begins to cool, very often it won't come back on again with the same failure.

I never see a failure with the raditors working on their own. I constantly see failures with running hot water with the only solution as described above.

Has anyone any pointers that I could run past my plumber? We know it's not a pump failure or low pressure, especially when the radiator circuit works perfectly.

Thanks a mill.

K.Flyer

Errrm....
Flashing 60 for Low Water Pressure or Circulation (pump) Problem, and he changed the PCB.
Why?

Do you have a Combi Boiler, (no hot water cylinder)
Or a standard system with a hot water cylinder and a time clock which has separate hot water and radiator controls.

lansing

Errrm....
Flashing 60 for Low Water Pressure or Circulation (pump) Problem, and he changed the PCB.
Why?

Do you have a Combi Boiler, (no hot water cylinder)
Or a standard system with a hot water cylinder and a time clock which has separate hot water and radiator controls.

He figured it was a false error and the electrical signal to get the boiler to heat was faulty. It's a standard enough system. The tank is an ACV tank and have separate clock controls for water and radiators.

My limited rational would suggest that the fault is something that is common between both water and radiators as somehow I can bypass the fault by turning on the radiators. But as soon as hot water cools and tries to kick in again I need to repeat turning on the radiators. What has us stumped is why does this only happen on the water circuit. Cheers

K.Flyer

I know you say intermittently and it only starred last year, but I would srart by double checking all wiring on the exterior controls / zone valves / stats etc., making sure that that everything is wired and signaling correctly.
If your plumber is not fully familiar with how the wiring should be, you will save money and time getting a RGI that does.

lansing

I know you say intermittently and it only starred last year, but I would srart by double checking all wiring on the exterior controls / zone valves / stats etc., making sure that that everything is wired and signaling correctly.
If your plumber is not fully familiar with how the wiring should be, you will save money and time getting a RGI that does.

Thanks for the suggestion. To be fair to the plumber the electrics was the first thing he checked. When the fault was initially showing he did troubleshoot the thermomstats and motorised valves. Could it be that the replacement PCB is also faulty or is that just too much of a coincidence? The failure on the original PCB and the new PCB are similiar but not quite the same. The old PCB had far less frequent failures and the new PCB needs this extra step of turning on radiators in parallel to get the hot water running.

K.Flyer

If you turn on both the radiators and hot water at the same time and leave them on together, does the boiler keep running as usual, or does it revert to the fault?

lansing

If you turn on both the radiators and hot water at the same time and leave them on together, does the boiler keep running as usual, or does it revert to the fault?

I haven't tried that but that would be a good test. I'll give it a go later tonight. My suspicion would be that the hot water will fail to come on unless one of the radiators is actively firing the boiler at the precise moment the water will try to kick in. This would go back to the water only coming on once I get the raditors to fire the boiler.

Keep in mind, the water is usually (but not always) capable of turning on from a cold start on its own with no need to turn on the raditors. However after it cools it mostly likely cannot fire the bolier again without the radiators. Just another angle to keep in mind!

Thanks for the suggestion.....

K.Flyer

It may be the windings in the hot water zone valve motor breaking down. Fine for the first go but just not pushing far enough to bring in the switched live after that. I see that problem more often with older Myson valve actuators.

lansing

K.Flyer wrote: »

It may be the windings in the hot water zone valve motor breaking down. Fine for the first go but just not pushing far enough to bring in the switched live after that. I see that problem more often with older Myson valve actuators.

Not sure what brand my valves are but can check later.

I can try to manually override the valve when I see the boiler trying to kick in on a hot water only heating cycle. It usually takes maybe 10 seconds to try to kick in before going into fault mode. If I'm quick enough I should be able to manually turn on that valve and see if the boiler kicks in.

However, how would the current fix of turning on the radiators help get around this?

lansing

Hi, back again to this issue with the Baxi boiler. I still haven't found the exact source as to why the 60 degree light flashes when trying to fire the boiler with the hot water circiut. In fact the issue is a lot more frequent. 99 out of 100 times I try to turn on hot water it will now no longer fire the boiler, resulting in 60 degree light flashing. I can get around this by turning on radiators first to get the bolier working and then turn on hot water in parallel.

As suggested by K. Flyer above I have replaced the motorized valve but the problem remains. The shaft on the valve itself seems free so its not stuck. I also notice that the hot water will only kick in now if the boiler pump is running. If the pump is off before I turn on hot water it will never kick in. If the pump is on before I kick in the boiler it fires every time. I don't see this issue with radiators, the boiler always fires with pump on or off.

This must be an electrical fault somewhere. Anyone got any ideas? Could it be a PCB fault? Thanks

lansing

Thanks for the suggestion. However my RGI had already checked the flow switch and replaced the diaphragm. I'm not sure if he specifically checked the bypass. However if this was the issue would it not be an issue for radiators too? Isn't this all common for all heating, not just hot water?

DGOBS

Can you tell us 'exactly' what he did with the flow switch? (other than replace the diaphragm)

How is the flow switch pin responding when your getting the 60? fault? (moving quickly out to make the electrical flow switch, moving slowly out, not moving all the way out, slow to retract when pump turns off)

Devil is in the detail.

lansing

DGOBS wrote: »

Can you tell us 'exactly' what he did with the flow switch? (other than replace the diaphragm)

How is the flow switch pin responding when your getting the 60? fault? (moving quickly out to make the electrical flow switch, moving slowly out, not moving all the way out, slow to retract when pump turns off)

Devil is in the detail.

To be honest I don't have those exact details. I do know he checked to see if the flow switch was sticking and he didn't think there was anything to suggest it was faulty. You'll have to excuse my ignorance but if it was the flow switch wouldn't it be an issue for radiators too?

K.Flyer

The flow switch would be a common denominator in the grand scheme of things, but should still be checked both visually and with a multi meter in both operating modes.

lansing

Here is another nugget of information:

When I mentioned earlier that we replace the motorised valve I should have clarified that we only replaced the head, not the the actual pipework. I wanted to see if the mechanical valve was sticky. I removed the head of the motorised valve and manually turned the valve (small shaft) into the "on position". I left the head of the motorised valve on the ground, unconnected to the pipework but electrically connected to the boiler. Then I turned on the hot water clock......again the boiler failed to fire with the valve permanently opened. So I concluded this valve cannot be sticky. Even when forced open it didn't fire. However if I put the valve into the "off position" with the head unconnected, the boiler will fire every single time, no problems at all even from a cold start. Obviously the cylinder isn't getting any hot water but it was interesting how the boiler fired. Then I tried it again with the valve opened, I could tell the bolier wouldn't fire (as expected) so I quickly rotated the valve to the off position, the boiler fired and when I quickly rotated the valve back to the on position it stays fired.

Conclusion: When it is boiler only circle the boiler will fire, when it is Boiler and Cylinder circle the boiler will fail to fire unless the pump is running.
Does this point to anything in particular? Thanks for the help.

K.Flyer

I am I right in thinking that the zone valve has 3 pipe connections to it?
Did you say you put a brand new zone valve head on the valve, or just took the original one off and put it back on again?
Sounds to me like a wiring issue.

lansing

K.Flyer wrote: »

I am I right in thinking that the zone valve has 3 pipe connections to it?
Did you say you put a brand new zone valve head on the valve, or just took the original one off and put it back on again?
Sounds to me like a wiring issue.

The zone valve has 3 pipe connections but one of them is blanked, so it effectively only has 2 connections. Essentially its a one input/1 output setup with the valve turning on/off the output.

Yes this is a brand new zone valve mortorised head. It made no difference, same failure signature.

Don't think it is wiring as this is unchanged from the original installation and worked perfectly for years. The head was replaced like for like so the wiring is identical.

In my own novice way I am begining to think it is a flow issue somewhere, like something is dirty or half blocked. This issue has gone from intermitent to now almost permanent which would suggest a flow problem to me. Is there a return filter from the cylinder to the baxi boiler that could be blocked? Could explain why the boiler and cylinder together won't fire but the boiler on it's own will from the hot water switch.

lansing

RGI was here this morning. He upped the pressure in the boiler thinking maybe that there wasn't enough pressure to push the flow switch in hot watre circuit. Still got internittent failures. He cleaned out the flow switch, filter and bypass. Still got intermittent failures. When the failure occurs he said the flow switch wasn't coming on but the shaft to push it looked like it was fully out. He could push the switch closed with a screwdriver. Only conclusion is that the flow switch is faulty but why it works perfectly with radiators is a mystery.