HW but no CH ??????

[dfranklin72]

Christmas Eve my boiler started playing games. The hot water and central heating would just stop. When the boiler was fired up it made clicking noises and the fan started. That was it. If you left it alone for maybe 4-8 hours it would come back to life. So a cold Christmas... I eventually got a plumber round and he told me that I would need a new PCB. He seems to check the valve and air pressure switch, which he deemed to be o.k.

So a went a head and installed a new £150 pcb in my Potterton 80e. Nothing changed. He was stumped. I was stumped. Although eventually the boiler did spring back into life some point during that day.

This morning the boiler was off. The CH was off but the HOT water had been running. I noticed that if I turned the HW to off and then back on again the boiler would fire up for 10-30 seconds and then stop. I tried turning the CH to on but now there is nothing. No fan or clicks.

One more thing, maybe a little irrelevant, I have been getting a lot of air out the system through the rad closest to the immersion heater?

As I said earlier the boiler is a Potterton 80e with pump feed supply. The pumps are working but get very hot.

Any help would be much appreciated.

 

[ChrisR]

The clicking is a common sign that the pcb needs replacing but it seems you've been left with an intermittent fault, which of course is hard to diagnose especially from a keyboard. These are quite simple boilers though so any boiler chappie with it in front of him shouldn't have too much trouble finding the problem, if it IS in the boiler.

If you're getting problems with HW working but not CH. then the motorised valve(s) would be suspect.

 

[dfranklin72]

Strange thing is The PCB was replaced a week ago and this made no difference. Are you suggesting that I should speak to another Plumber? The one that came round was a corgi-registered plumber? If you are saying that the boiler is pretty simple then do you think the problem could be the electrics? I have checked all the wiring and tested the live and switched circuits and they all seem to function correctly. When the HW is switched on the Switched live comes on but this is not the same on the CH. Dose the Valve have to open for the switched live to come on?

Dan

 

[MANDATE]

Yes! With a 3 port mid position valve the live to boiler /pump comes from the cylinder stat for HW only positon.
For the CH only position it comes from the room stat via the actuator head of the valve. But it goes through a micro switch.
Could be motor does not turn actuator far enough to operate microswitch or microswitch is faulty.

I think you should be able to move valve with lever to the CH only position. If boiler operates it suggests motor problem, if not then microswitch problem.
What valve do you have?

 

[dfranklin72]

I presume you are talking about the motorised valves.

I have two located in by the pump. i switched both to manual but nothing happened.? Do you think this is the problem? They are Honeywell F4-9517 models.

Dan

 

[punchjoshua]

sounds like your three way valve has had it ie no ch but hot water/

 

[MANDATE]

Looks like yours is not a 3 port mid positon valve used in a 'Y' plan.
You appear to have two zone valves, one for HW and one for CH.
I believe they also have a microswitch to feed power to the boiler/pump when the valve has gone to the open position.
You should be able to hear or maybe feel if the motor within the valve head is operating
I think I would be looking to see if the actuator head could be removed without causing any problem, this would help, because you could turn the spindle by hand to the open position and then some hot water would pass through it when HW only is demanded. This would prove the valve actuator is not functioning correctly or is no longer wired correctly.
I've had a potterton (3 port)valve head off the spindle, turned it upside down and watched it operate correctly, but with no output voltage. This was traced to dirty contacts within one of the microswitches.
I have no knowledge of your valves, but If it is not opening or the microswitch is faulty then I think it would give the problem you have.
Do let us know how you solve the problem

 

[dfranklin72]

You are correct. My mistake. I am learning what’s what so please bear with me. I have 2 way valves.

Last Night I when home and switched the HW to the on position on the timer control. I then went to the 2 way valve and manually switched it to the on position. I had hot water and CH. I am not sure why this happening but at least last night was bearable. I spoke to the plumber that initially told me to replace the PCB and he thinks its now an electrical problem. I have an electrician calling tonight but not sure if this will help.

If I turn the CH on the Timer to the On position and Manually switch one of the valves then nothing happens, even if the HW is set to on.

It sounds to me like the valve is not opening to send the signal back to close the switched live to fire the boiler.

Dose this sound o.k. or am I barking up the wrong tree.

Just for reference I would like to know why I have two valves. Is there a good reference site to look at so I can get a better understanding?

Anyway, Thanks for all your help so far

Dan

 

[ricarbo]

Americans like to put in 2 two port valves. Brits like to put in 1 three port valve. I don't think either is better, but one valve is cheaper than two. Two port valves easier to wire when you have more than two things to heat e.g. two heating zones plus hot water cylinder. You can test that the two port valve micro switch (the proving switch) is working, by powering it up and checking if mains live appears at one of the other cores of the multicore cable to the valve head, after while (max about 30 seconds). Operating the manual override probably won't do this. If the head is faulty, you can replace it without opening the hydraulics or changing the whole valve.

 

[dfranklin72]

Well it’s off again. This time the faulty thermostat has been replaced along with both of the 2 way valves. Yesterday the heating developed the original fault. No HW and No CH.

I have again checked the valves, pump and all the electrics which all seem to work fine. I have tested the Boiler stat, the air pressure switch and had my electrician test all again. When the failure occurs it is not sending a live to the gas valve. Is there anything I have missed that stops this happening, bearing in mind that I have also replaced the PCB which is being switched live on start-up procedure.

Any help would be grateful before I rip the whole system out and get a combi (not Potterton)

Dan

 

[Softus]

Americans like to put in 2 two port valves. Brits like to put in 1 three port valve.

Is this conjecture, or has someone conducted a survey?

I don't think either is better, but one valve is cheaper than two.

...until the 3-port goes wrong...

You can test that the two port valve micro switch (the proving switch) is working, by powering it up and checking if mains live appears at one of the other cores of the multicore cable to the valve head, after while (max about 30 seconds). Operating the manual override probably won't do this.

Er, yes it will.

If the head is faulty, you can replace it without opening the hydraulics or changing the whole valve.

Not on all valves you can't. Which you would know if you were a heating engineer, or had read enough topics on the forum.

Beware of giving false advice.

 

[dfranklin72]

Thats all very well but it makes no deference if you have replaced these items already. My system is beginning to be a bit like "triggers broom".


It came back on again about 5 hours after it went off. There doesn't seem to be ny pattern to this though.

Tried calling Potterton again yesterday but after holding for 1.5 hours gave up in the end.

As for the advice, any advise is better than none.

 

[Softus]

I don't agree that no advice is better than poor advice.

Your symptoms are consistent with a boiler fault. An electrical fault elsewhere is possible, if the boiler is behaving like it's dead, but since work has just been done on the boiler I would continue fault-finding that.

There is a fault-finding process for this boiler. Have you followed it?

See http://www.partsarena.com/baxi/.

And just because it has a new PCB doesn't mean that the PCB isn't faulty. For one thing, if the pump is faulty then it's capable of damaging the PCB. but the heating engineer you've used should know all of this...

 

[meldrew's_mate]

Lots of work seems to have been done, but without a clear objective. I suggest the following course of action:

1. Turn on the HW only, does the valve open fully and operate the end switch? If it's quiet you will hear this as a single click about 10 seconds after the HW is turned on.

2. Assuming stage one is OK turn the DHW thermostat (on the cylinder) down until it clicks (off). Listen for the whine of the HW valve returning to closed position, this takes about 5 seconds.

3. Turn the cylinder 'stat back to normal and listen again for the click to indicate it is open. Now go to the boiler and check for 240vac at the SL input. If it's there the boiler should start. If not you have a boiler fault, if there's no SL input you have a wiring or HW zone valve fault.

4. Repeat stages 1,2,3 with the HW off and the CH on, using the room 'stat to open/close the CH valve.

A common problem with the two port valves are burn-out of the synchronous motor, an easily replaced spare part.

As for the boiler, once the peripherals have been sorted out, it is common for the fan to run for 20 seconds or so before the ignition process starts, longer may indicate a failing fan.... please repost when you have determined whether it is a boiler fault or not.

You have previously stated that you have "switched live" at the boiler, therefore I assume you have enough competance to make the measurements safely.

 

[dfranklin72]

i can see where you are going with this but when the fault happens it effects both HW and CH. The valves open even when the fault occurs and send the SL back to the boiler.
I here the click as you mentioned when the HW or CH is turned on both valve operate but the boiler just will not fire up. I have noticed that there is a lot of air in the system. If I bleed the radiator nearest to the boiler after the problem occurs it released a lot of air, maybe 30 seconds. This may be a result of the pump pushing water but not being heated?

So if it’s a boiler fault then what’s the next stage? Replace?

Dan