Diagnosing cause of boiler not diring for heating - programmer?

[stuartb3502]

Hi,

• Potterton boiler
• Potterton EP2002 programmer
• Honeywell room stat
• Stat valves on rads

All on an install which has been working and untouched for many years.

I'm after a bit of help to narrow down a fault. Our boiler is not firing up all the time even when programmer is on and hall based thermostat is set way above actual temp. It has been intermittent and if I turn off and then on at the programmer it will often come on. Today that wouldn't work either. Switching heating on fires up the boiler with no issues. When I then switched heating off and then tried the CH that fired up the boiler too.

Reading so far seems to suggest that this could be a sticking relay in the programmer. I'm leaning to replacing the EP2002 with an EP2 which is a straight swap on the existing backplate. We are planning to move house this year so not worth swapping to more sophisticated solutions.

I'd just like to be able to be sure it's the programmer before spending £80 on one. Any tips? I am capable of using a multimeter and working safely. I haven't had the programmer face off yet, but imagine that I could check output of CH relay assuming it's fairly obvious where that is when get the face off.

Thanks very much,
Stuart

 

[Harry Bloomfield]

Is this an open vented system (header tank in the loft) and a 3 port valve?

It could be the valve / valve actuator jamming. Try giving the actuator head on top a gentle tap/ try taking the head off and taping it.

The way it works is the EP2002 tells the valve to open, the valve once in the correct position, then tell the boiler to fire.

 

[stuartb3502]

Thank-you for the suggestion.

I believe it's open vented (the hot water is a pressurised Megaflo), but there's a header tank in loft. There are two motorised valves, but I'm not knowledgeable enough about how the CH is piped to know which is which (any tips for identification - follow the pipes I guess?). Of course the boiler is working right now so I can't do a quick tap test to test whether the valve is sticking, but will do when the fault occurs again.

Thanks.

 

[stem]

If you are able to do it safely, you can remove the EP2002 and first of all check that the wires in terminals L, 4 and 5 are securely fixed. They are the wires responsible for controlling the heating.

As a test, again, if you can do it safely, you could insert a link wire to join together EP terminals L and 4 (CH ON)

That will by-pass the heating control and put the heating permanently 'on' (the room thermostat will still be working) if the problem is still manifest then it's not the EP2002, If the problem has gone away, then it is the EP2002

 

[stuartb3502]

Hey - thanks very much. Yes - that makes sense. Will give it a try when the problem next occurs.

 

[ianmcd]

Good chance it will be the EP they are not very reliable to be honest

 

[stuartb3502]

Thanks Ian - will report back when I know.

 

[Harry Bloomfield]

There are two motorised valves, but I'm not knowledgeable enough about how the CH is piped to know which is which (any tips for identification - follow the pipes I guess?).

If you feel the pipes, starting from cold - they will get hot when you create a demand for heating, or hot water.

 

[stuartb3502]

Thanks again for all the help everyone - really appreciated. I found that the motorised valve on CH was making a pulsing/buzzing sound when trying to open. A tap on the valve seemed to get the valve open and the boiler would kick in (sometimes taking a few gos). Problem was still too intermittent to try some of the systematic diagnosis steps suggested here. I took a punt that it was either the motorised valve head starting to go and not quite fully opening (and thereby closing the microswitch) or the valve itself was getting stuck on some crud. Decided to buy a new motorised head as I was capable of trying that. Could have bought just the motor itself (£21-35) but opted for the Honeywell replacement unit at £55 in case something else was faulty. Swapping was easy (I turned the mains off fully at consumer unit since I could not be confident how to isolate the junction box otherwise). It needed a torx bit (although flatblade would also suffice) and small/electrician's flat blade for the terminals etc (quite a few Youtube videos and fortunately these Honeywell valves seem like a de facto standard and therefore easy to get). Just tested and it's working fine, but won't know for a couple of days whether it's fixed due to intermittent nature of issue before.

 

[Harry Bloomfield]

Decided to buy a new motorised head as I was capable of trying that. Could have bought just the motor itself (£21-35) but opted for the Honeywell replacement unit at £55 in case something else was faulty.

If the actuator was moving at all, the motor is OK. Plenty of time now, for you to look around for a spare actuator at a good price - ready for next time