Potterton Promax He not reliably providing HW.

[mikesin]

The boiler was installed about 9 months ago. It replaced a conventional potterton and was 'dropped in' on existing pipework - the pipework is like most old systems - extended and fiddled with over time.

Problems existed from day 1 with reliable operation of the system. Over time the pump and the diverter valve were replaced. System would work for a day or two and then back to unreliable operation with lockout occuring - boiler indicated incorrect or reversed flow. A day of detailed work found two faults, - 1 with the cylinder stat and 2 with the return from the DHW cylinder being connected to the boiler flow. These errors were corrected - all was fine for about 3/4 weeks.

Whilst the parents on holiday the son reported that the boiler had stopped creating DHW Investigation shows boiler not firing up if only DHW is set on with programmer. If Ch is active as well, or CH only, boiler fires up fine.

As a test I set DHW on, manually operated diverter valve to mid position and the boiler then ran without problem - however having CH on when outside temp is 25C is not nice!

The return pipework from the DHW tank to the boiler starts off in 22mm, reduces to 15mm and then joins CH return at boiler - the CH return is 22mm. Could this create a problem in circulation. ??

I ask this becaues when the boiler fails to start with DHW only being demanded, the circulation pump is running but I cannot feel any difference in temp at the boiler between the flow and return pipework. Occasionaly the boiler will light for around 20 seconds and then shut down. An occasional click is heard but the boiler doesn't light

I am of a mind to replace this section of 15mm pipe with 22m but is is going to involve taking out a bath because of the way the pipework has been installed and then the bathroom rebuilt at a later date. Thoughts appreciated

I have checked out wiring and operation of diverter valve/pump/cylidner stat and thermostat as detailed in another post on this forum (CH programmer or motorised valve t-8369) and confirm wiring and operation of valves etc is correct.

 

[Agile]

Why do I get this feeling that you installed the boiler but you are not CORGI registered?

My immediate reaction is that the boiler is not correctly wired to the system or even the pipework to your "diverter valve" is incorrect.

Did you power flush the system and what inhibitor did you use?

Tony

 

[mikesin]

Tony, its my brother in laws boiler. He installed and had the installation checked by a Corgi registered guy.

The diverter valve wiring is absolutely correct according the to the post on this website that I referred to in my initial post. it peforms all of the corect manouveres according to the external signals i.e CH stat or cylinde stat and sends the correct voltages down the correct wires.

The system has been draind several times as various items have been changed and there is no sludge or corrosion showing in the removed items. The pump is in the flow from the boiler circuit and then it presents the hot flow to a diverter valve that offers either flow to DHW into the HW cylinder or flow to the CH circuit or in mid-position to both.

There is an automatic air vent at this point.

The pipework was incorrect as you suggest but now that the return from the DHW cylinder circuit is connected to the CH return all is correct. However the return from the DHW cylinder leaves the cylinder in 28mm and is soon reduced down to 15mm, joining the 22mm CH return close to the boiler - could this reduction cause a problem of insufficient flow through the boiler for it to light up ?

I have tried the system again today but apart from a brief light up for about 10 seconds the boiler is not responding even though the pump is running as I have set the cylnder stat to about 60C - the immersion heater has been on so the water in the cylinder is hot. As the pump is running the flow and return at the boiler are about the same temperature presumably becaues the circulating water is being warmed up by the hot water in the cylinder . I have told my brohter in law to leave the immersion off to see if the boiler will respond to the eventual drop in cylinder water temperature. Our next move is to get BAXI back to check the boiler as it is under warranty.

 

[DP]

If the boiler was ‘dropped in’ onto existing pipes, how could the connection at the cylinder (though these should not effect boiler operation) suddenly become reversed?

Y plan is essentially two circuits side by side. Would suggest you check out the wiring. It is easy for someone working with Y plan regularly to slip up. Heaven help someone who has not wired one before.

If boiler fires for 10 seconds and then shuts down, it is possible, one of many alterations has resulted in flow and returns ‘shorted’, or even the controls not fitted correctly. My bet is on the motorized valve fitted/ wired incorrectly.

Draining a system several times does not remove sludge lying in the valleys. You can fill and flush many times, but sludge at the base of the radiators will only move if 1) the radiator is removed to the garden and manhandled whilst water is passed through it, 2) power flusher used in accordance with makers advise, 3) chemicals are used. If you take a water sample and send it to Fernox or Sentinel, they will for a fee, carry out water analysis. You will be pleasantly surprised to learn that the system water is more than likely, still ‘sedimented’.

If you have installed the boiler or system controls incorrectly, do not be surprised when Baxi bill you for putting the matters right. In warranty call is for those instances when the appliance itself has a defect on it. Makers can ask for visual of the Benchmark Logbook.

 

[meldrew's_mate]

The boiler was installed about 9 months ago. ....A day of detailed work found two faults, - 1 with the cylinder stat and 2 with the return from the DHW cylinder being connected to the boiler flow. These errors were corrected - all was fine for about 3/4 weeks.

...Investigation shows boiler not firing up if only DHW is set on with programmer. If Ch is active as well, or CH only, boiler fires up fine.

As a test I set DHW on, manually operated diverter valve to mid position and the boiler then ran without problem ....

...I have checked out wiring and operation of diverter valve/pump/cylidner stat and thermostat.

Possibly the cylinder 'stat has been wired wrongly. as the system works when the motorised 3-port ("diverter") valve calls for heat. On hot water only duty the "call for heat" signal (measured between the orange valve lead and neutral) is provided only from the programmer terminal 3 via the cylinder 'stat. Turning the 'stat up and down whilst measuring at the orange lead will confirm this :- no signal = no boiler firing.

It's also worth checking that the programmer has been mounted properly on its backplate or a poor contact may result in unreliable operation.

Check the pump is clear of sh1t and debris, 4 weeks is plenty of time for the impellor to block on a dirty system, causing low flow and subsequent boiler short cycling. The Promax also has a flow sensor on the flow pip[e at the top of the boiler, if this is not effectively bled of air it can stop the boiler working (and CH normally flows greater than DHW). If you feel competant try slowly undoing the large nut to see if any air is trapped - the solution then would be better air bleeding (pipework design)

 

[Agile]

I seem to have been pretty accurate with my guesses so far!

I dont think there is anything wrong with your boiler.

There is no point in checking anything when the cylinder is hot because there will be no demand for heat.

Start with a cold cylinder and feel the pipes to see where they are hot and cooler.

The 15 mm tube on the HW will have little effect when HW only is in use but will greatly extend the HW recovery time when CH is on as well.

If you call BAXI it will probably be a chargeable call as the boiler is OK as far as I can tell.

Tony

 

[mikesin]

Baxi confirm nowt wrong with boiler - all wiring and controls ok - have drained some water out of system and added sludge remover solution. Boiler fired up fine with both DHW and CH calling for heat - will leave it all running for a few days to circulate the cleaning fluid then will drain down, refill, add inhibitor and hope for the best.

Thanks for the comments and ideas so far - will post with results.

 

[gazthepottertonengineer]

And i bet we didnt charge you either god we are soooo nice

 

[gazthepottertonengineer]

no wonder we are the number 1 boiler manafacturer in the UK