Open vented system, No HW, CH works fine, BAXI 80HE boiler shows Dry Fire after every restart

[fandyman]

The boiler is going to Dry Fire after every switch off and on most of the times apart from when the rads are on.

Btw I usually have CH and HW on constant ON throughout the year which is not very good I suppose.

 

[Deleted member 267285]

@CBW Hmm my Drayton termostat is constantly on for HW and off for CH now.

That’s your programmer, not a thermostat, but still what I asked about. So, obviously pipe B is cold then? Cylinder thermostat is turned up to 60?

 

[fandyman]

Yes sorry I meant to say programmer.

Pipe B is cold and cylinder thermostat is at 60C yes.

 

[fandyman]

Also the only time pipe B gets warm is when rads are on and then B and A gets same level warm.

 

[Deleted member 267285]

Also the only time pipe B gets warm is when rads are on and then B and A gets same level warm.

It does point towards the motorised valve. The dry fire fault could be a circulation issue, which could still be your hot water fault, but unlikely if it’s getting through on heating together with hot water.

 

[fandyman]

Could it be the motorised valve is stuck in the CH position and the B pipe gets warm from heat transfer from A?

 

[fandyman]

Hmm but it would not get same level hot I suppose - it wouldn't make sense.

 

[fandyman]

One other thing I noticed on the motorised valve is that I cannot make the lever latch into a notch in the casing to keep it open. Not that it changes anything but maybe someone knows if it is relevant here. Maybe that indicates the valve is gone?

 

[fandyman]

Also what I do not understand is that when the motorised valve fails it is usually CH that does not work with HW working but my case is the other way round which baffles me.

 

[fandyman]

@CBW Would you suggest doing another check anywhere?

Is it possible to connect the system to the mains or drain and refill the system to rule out any blockages?

 

[HERTS P&D]

Fit a new 3 port valve.

Andy

 

[fandyman]

Thanks @HERTS P&D. Am I able to change it myself (I am fairly handy DIYer) or shall I wait for an engineer (from which all are busy) until they become available next week?

 

[HERTS P&D]

If you can do it yourself, then crack on.

Don't forget to take a picture of the wiring and join the wires one at a time. You could always get a connector block and join the wires without going into the 10 way.

Also don't forget new inhibitor.

Andy

 

[fandyman]

Thanks @HERTS P&D.

Just before I crack on is there any possibility it is not that part that's causing the issue? I know that all the signs are pointing towards it but want to make sure I check everything before I change the valve.

 

[Harry Bloomfield]

Just before I crack on is there any possibility it is not that part that's causing the issue? I know that all the signs are pointing towards it but want to make sure I check everything before I change the valve.

Sometimes, the actuator, can be swapped separately, to the actual valve under it.....

An additional check you might make, if the actuator is removable, is to try turning the valve spindle directly. You should be almost able to turn the spindle, with just your fingers, but will turn quite easily with a pair of pliers. If that seems OK, and allows hot water through to both ports, and if you can source just the actuator/head/the motorised valve part - you can get away with just changing that. It will avoid the need to drain down, and change the valve.