Hot water but no heating with Potterton Netaheat Electronic

[dradambbb]

Hope knowledgeable people can help on this one as they have in the past. Thanks to this list I've fixed at least 2 boilers.

Recently moved into a place with this oldie but goodie boiler which worked fine for HW and CH till a few days.

HW is still fine - coming on/off from the Honeywell control panel and is also controllable via the thermostat knob.

Boiler does not come on when CH is activated from controller. I hear a microswitch click from the controller but the boiler does nothing. I checked the overhead cold water tank that feeds the boiler - it was empty. Refilled it. Can see why water to it was turned off at the tap - the float operated valve does not close water off fully resulting in overflow onto balcony. I refilled the tank but still no go for CH. Note that one radiator still warms up when HW is on thanks, presumably, to the heat exchanger.

Given that this is not a fully sealed system I thought there may be some airlock preventing detection of adequate pressure. (There is no pressure gauge.) If that is a cause - I didn't see any instructions in the install/service manual. Also the diagnosis chart does not mention my scenario so can't do the dumb old follow-the-graph-to-the-cause approach.

Suggestions please? Much appreciated.

 

[Agile]

Look for a faulty zone valve on the heating circuit!

Those boilers may be reliable but they are very inefficient and overdue for replacement. But with limited parts availability and only a very few ( like me ) prepared to repair them there will be less and less repaired any more. Some contain asbestos too.

Tony

 

[ianmcd]

As Tony said unlikely to be a boiler fault more likely to be an external control zone valve fault or room stat fault would be my guess but without more information it is simply that a guess

 

[JohnD]

is the pump turning?

 

[dradambbb]

Thanks for the responses so far. Incidentally here's the manual http://www.partsarena.co.uk/baxi/System/DATA/Dx/DS1/installation/2508/I19-2508/I19-2508.htm

I will check the zone valve. Does its state form an input to the boiler electronics? Can't see it in the manual.

There is one room thermostat though I am unsure that it is connected. It's set high though just in case.

There are two pumps. I guess the set-up is as per fig 25 of in the link. The HW tank and pumps are located in a separate part of this large single floor apartment so I won't know if it is running until I place my hand on it to sense for vibrations. At this moment I am suspecting that it is not running during CH operation.

Based on your responses I take it that you think the absence of water in the water container fitted above the boiler is unrelated or unlikely to be related?

Thanks,
Adam

 

[Agile]

The fault is probably unconnected to the lack of water in your F&E tank.

There are many different ways of providing CH and HW and we have not seen your system.

Motor valves are often used as relays to bring on the boiler and pump.

Tony

 

[dradambbb]

Thanks, Tony, Will be checking the zone valves tonight.

 

[dradambbb]

The set-up is one 3-port Honeywell ZV sitting on top of a pump and one 2-port Honeywell ZV sitting on top of another pump.

For the 2-port set-up (going from water tank to under the floor) neither CH nor HW operates it. However, the ZV seems to operate fine in terms of lever resistance: no resistance initially and pushing further against the spring opens the valve. Releasing the lever closes the valve as required.

The 3-port Honeywell ZV that does not seem to be operating 100% per spec: initially the lever for manual override moved the full way. I was anticipating resistance to kick in at least half way through. Switching on CH produces a clicking whirring sound like an old clock or think timebomb. (!) With HW on there's resistance in the lever but moving it can make a horrible whirring sound. The pump below this ZV comes on only when HW is on.

Sounds at least like the 3-port ZV needs to be replaced. Given that this valve is old, can I replace the motor without replacing the valve assembly? I read that for older 2-port Honeywell ZVs this may not be the case.

Many thanks,
Adam

 

[dradambbb]

This is just a follow-up to say that the problem has been solved today.

Thanks to Agile's initial advice I purchased a new 3-port Honeywell mid-position zone valve, drained the tank and the boiler (mostly on the floor, ahem, ), removed the old unit and fitted the new.

Draining the tank was a pain. Next time I'll use a hose connected to the drain cock rather than a painting tray.

The whole assembly needed replacing because the original item was a very old unit on which unscrewing just the powerhead lead to leaks from the mounting screw holes. I was unable to prize off the compression rings from hose ends so ended up reusing them. They seemed in an okay condition. In automotive applications this usually leads to leaks but here all seems okay so far. Will recheck in due course and retighten if necessary.

Cheers.