Strange CH fault

[JohnBailey]

Hi, I'd appreciate some advice about a strange fault that happens occasionally (yesterday), it probably occurred 4 times last year.

When it occurs, I get home from work to find the house is really hot and the hot water is way too hot, dangerously so (it's funny how the ladies in the house don't seem to notice the extra warmth!). If I switch HW and CH to off at the programmer nothing happens, the boiler and pump keep working heating house and water. I get round it by switching the mains switch to off taking power off everything which resets everything.

I believe it only happens when the heating is on, as throughout summer the HW works OK and never keeps heating just the cylinder.

The boiler, programmer and mid-position valve were all new in spring 2010, Broag Remeha Avanta, Drayton Lifestyle, Drayton MA1, all installed by a registered fitter. At the time of installation he seemed unsure of the wiring and said he would get an electrician friend to check it, I don't recall that this actually happenned, but I guess it must be correct as it works as it should for the majority of the time.

I have since had the boiler serviced by a more local (registered, and Broag-Remeha trained) plumber and asked him to check the wiring (explaining my worry) and I described the fault to him. Of course everything looked and behaved perfectly for him so all he could do was check the wiring which was OK.

I'd like to be sure about the cause of the problem so that I could ask him to replace [whatever], and am guessing that the boiler and pump are dumb items that just do as they're told, and I'm sure the stats are ok, so the problem is likely to be something that is in control ignoring the inputs, which comes down to the controller or the MA1.

Does anyone have any suggestions?
Regards
John

 

[linkyplumb]

I have had this on a few of these broag boilers. Was the link wire removed from the control board?

 

[MANDATE]

Are you aware that when the HW and CH are both switched off at the programmer, there is still power going to the valves grey wire from the HW OFF terminal on the programmer.
I would think the problem must be related to the valve head

 

[dcawkwell]

central heating 2 port valve sticking on.

 

[Agile]

central heating 2 port valve sticking on.

That seems unlikely as there is only a three port valve!

I agree that it sounds like a motor valve problem.

Replacing the head is a relatively cheap repair.

However as its only every three months is it really worth the problem?

You can check the valve by learning what the lever feels like normally and then comparing it when the fault occurs!

Tony Glazier

 

[JohnBailey]

Thanks folks.

Is the sticking valve likely to be in the head part rather than the valve part? If so, would a squirt of WD40 make any difference, or do any harm?

John

 

[D_Hailsham]

Are you aware that when the HW and CH are both switched off at the programmer, there is still power going to the valves grey wire from the HW OFF terminal on the programmer.

This only happens if the valve was in CH only position when CH was switched off by thermostat or programmer.

Although the valve stays in CH only position, the voltage on the orange wire is only about 100-150V, so it's not enough to operate the gas valve.