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Andrew Smith
Andrew Smith, HVAC Technician
Category: HVAC
Satisfied Customers: 3775
Experience:  Heating and Controls engineer
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I have an odd problem on my baxi solo. If the central

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I have an odd problem on my baxi solo. If the central heating is turned on , the water pump does not activate , however when the hot water is selected it does. As such the only way to get heat to the radiators is to have both the water and heating on... I am guessing its the PCB but before I go and get a new one I thought I'd get a second opinion.
Is the pump wired to the boiler or wiring centre?
Does the boiler run but the pump doesn't?
Customer: replied 4 months ago.
Hi, its wired to a wiring centre... program/timer also wired into the wiring centre, which is what made me think. that said the boiler comes on but wont run if the pump isn't running
Customer: replied 4 months ago.
There does seem to be a further problem now as seems to be ignoring thermostat (both room and water tank), so not delivering anywhere near enough heat to the radiators before switching off.. Feed pipes getting up to temperature (not overheating) but cyling on and off so radiators getting luke warm at best..
Customer: replied 4 months ago.
early start so will pick up again tomorrow.
No problem.
The boiler will run without the pump but will just keep reaching temperature and shutting down.
Can you check power to the pump?
Can you check the pump is actually spinning?
Customer: replied 4 months ago.
there is power to the pump, and as I say it only spins when hot water heating selected. Heat is getting to radiators , but shuts down before they get anything more than luke warm.
On the heating only option , no power is going to the pump and although the boiler shows on, it does not light. All points towards the boiler PCB .
Really don't think its related , but sllghtly coincidental is I changed a radiator pre christmas . Noticed quite a build up of sludge so treated with cleaner and flushed. There dont appear to be any blockages but re-flushing again as think there is still some debris moving around. 99% sure there are no air locks
Hot Water is getting to temperature pretty quickly and I can manually over-ride the divertor valve, so pretty much looks like its ignoring the inputs from the heating side of the program.. ie room thermostat.
The problem will be with your 3 port valve. This opens when told to and the internal microswitch then powers the pump and boiler.
Does it power open at All?
Customer: replied 4 months ago.
The microswitch effectively seems to have two settings, ie hot water only , or heating and hotwater. The microswitch does power between the two , and its currently set to heating and hot water. Not convinced the valve itself does anything any more as noticed during summer that a couple of the radiators upstairs got hot when only the hot water was on
That may just be heat creeper up the return pipe.
When on central heating only the vslve should be fully open so that the lever is slack
There are 2 sets of microswitches on a 3 port valve (mixed and heating only) when the valve is shut it is on hw only
Customer: replied 4 months ago.
OK that makes sense. So in effect what you are saying is while the physical control of the pump sits on the boiler PCB, it is most likely the fact the 3 way microswitch is not telling it that the heating has been selected.
Customer: replied 4 months ago.
Testing for that is a lttle tricky as the motor on the valve seems to be functioning , but I cant easily check if the microswitches within it are working ... ie if a signal is being sent to the boiler.
Customer: replied 4 months ago.
Will have a proper look at the wiring centre when I get home.
Customer: replied 4 months ago.
most likely will also move this to a call...!! chats are fine for the basics but think you may well have more questions..
In the wiring centre will be the best place to check.
You should see and hear the valve opening.
The pump will be controlled by the 3 port valve unless you have a pump overrun requirement.
Customer: replied 4 months ago.
the pump does have a 5 min overrun
A 3 port valve system is known as a Y Plan
Ok, then the pump live should be fed from the boiler (but the boiler still gets its go signal from the 3 port valve)
Like this
Customer: replied 4 months ago.
OK. Got it . Will have a look tonight and get back to you... As a job I suspect if the 3 way is the culprit then I will have to change the entire value as parts on a 18 year system seem to be quite hard to come by !!... Not the end of the world... just more of a pain than I was planning for !!!
Let me know the make and model of the valve or even a picture and I will tell you if it is a full valve or a simple head swap.
Customer: replied 4 months ago.
thanks will do
Hi, did you manage to take a picture?
Customer: replied 4 months ago.
Hi Andrew, looks like you are absolutely right. Tested by overriding the switch on the actuator, and sure enough pump came on, but no signal to boiler to turn on. The actuator is a Drayton Mid Position Actuator MA1. Not a whole heap of price difference between the whole assembly and just the actuator so will pop into screwfix on the way home tomorrow and swap it over. Do you mid if I leave this open and come back to you tomorrow night to confirm all working?
No, that's fine.
An easy one with 2 screws on the top.
Give the pin underneath a spray with WD40 and a wiggle with some pliars and try the head only first.
Come back to me tomorrow and let me know how you get on
Andrew Smith and other HVAC Specialists are ready to help you
Customer: replied 4 months ago.
Thanks , will do.
Ok, just reply tomorrow or it leaves the question open tbis end for others to answer
Customer: replied 4 months ago.
normal service has been resumed , thank you