Intermittent Central Heating Demand...

[monkeyboy67]

I seem to have an intermittent fault on my Baxi Solo 2 RS 50 boiler. When I demand central heating sometimes it works and sometimes it doesn’t. The hot water system is fine and the radiators do get hot when the system is running. I have fitted a new pump and also checked the pump overrun is working. The radiators are not fitted with local thermostats so the heating system is controlled by a controller in the hall. I have checked that this stat is not the source of the problem by shorting the two wires in the stat together (live and demand). I have noticed that sometimes if I switch off the electrical supply to the boiler and then switch on this sometimes allows the central heating system to come on – but this doesn’t work all the time. I have bought an overtemp thermostat but have not fitted it. The fully pumped system has a Honeywell 3 way valve fitted and I have manually locked this valve open so the central heating should be allowed to flow at all times. The demand on the timer is set to “On” i.e. on permanently. Pilot light runs fine. Any thoughts?

 

[ArtfulBodger]

So what is the boiler doing when there is a demand for heating and no heat? is the fan running at least?

your diagnostic methodology seems a little haphazard - so far you haven't identified the area of the problem, just the overall symptom

 

[slippyr4]

It's hard to tell from your post, so please don't be offended if this sounds a little patronising... But boilers have thermostats in so that they only fire when the water needs more heat. If you pump is running, and the heating is "on", if the radiators are up to temperature the boiler may well not need to fire all the time.

Do you actually have an issue whereby the house is too cold, the radiators are cold, and the boiler still won't fire? Or is it just that the boiler is not running permanently.

 

[monkeyboy67]

AB:When there is a demand for heat and there is no heat, the boiler is not running.... although I "think" i can hear the fan running....
s4: the house is too cold, the rads are cold, the boiler wont fire, when the central heating does run, the rads do get hot and the boiler toggles on and off as I'd expect... the fault being the CH doesn't heat the houise to the demanded temperature consistantly...

 

[weareleeds]

Try putting it on htg only to check diverter valve lever has moved (do not lock it in manual position) if it doesn't move then suspect synchron motor or actuator if it does move but doesn't fire then suspect switch in actuator head

 

[monkeyboy67]

Thanks guys... I think you've put me on to something...with the 3way valve manually locked open I get central heating when there is a demand for hot water...if I put the 3 way valve onto auto, I don't get any central heating at all. How fast does the valve motor open, I have no one to help at the moment so don't know if the valve has already moved by the time I have raced up the stairs!
PS I cant put my control to heating only, my selection is water only or water and CH...

 

[MANDATE]

Something don't quite add up in my mind! A fully pumped system using a 3 port mid position valve gives the choices of 'HW only' ' HW & CH shared' or 'CH only' so you should be able to select 'CH only'.
Has the valve got a number? eg V4073A.

 

[ArtfulBodger]

You need to work out from the wiring centre what is happening. For CH only you will have to have 230VAC on the grey and orange wires from/to the 3PV.

CH plus HW doesn't operate the valve in the same way.

In all probability you have a duff programmer or a wiring problem, so all the bits you replaced earlier was probably a waste of money.

If you need to replace the programmer, get a proper twin channel one