Had HW but no CH, diverter valve changed, now CH but no HW !

[daved]

Hi, hope someone can help me as i've had this problem now since new years day !

just before christmas my central heating started playing up, cold downstairs, hot upstairs. bled the system, including the valve by the water pump (read it elsewhere on here) no joy.

i had hot water although the boiler (potterton netaheat) occasionally seemed to go into shutdown mode (pardon my non plumbing jargon!) and had to be reset by pressing the little button underneath

having had same problem before when the water pump broke down i called out a plumber via a heating insurance contract that i have and within five minutes he had had diagnosed the diverter valve as the problem

after fitting the new valve i now have hot radiators up and down (albeit that down are not as hot as up) however i no longer have hot water. the water comes out lukewarm despite turning the temp controls up.

now when i switch the hot water and central heating on, the boiler lights
goes for a random amount of time (has been as long as a couple of hours) during which i get hot CH but lukewarm HW. It will then go into shutdown mode again and will light back up after a while once i'm able to press the reset button.

i asked the plumber about it and i quote roughly "you're getting air in the system that is going back into the boiler and sending the system into shutdown mode. this is because your radiators are blocked. its complicated to explain (warning bells sounded at this point) but the expansion tank up in the loft should fill up with water and is taking in air instead (he never went into the loft). the only way to resolve this really is to powerflush the system."

my query is this - is this a viable solution or should he check other things first ? i ask because as you can guess "BLOCKED ANYTHING / POWERFLUSHING" is not covered by my insurance policy which means i'll have to shell out 200 quid plus from what he said and having just had christmas and my sons first birthday to contend with, money is a bit tight right now if its something that i dont actually need to fix the problem.

no slight intended and total apologies if he's right but something in the term "its going to need powerflushing" suggested to me a scam similar to the blocked drain solution of "oh we'll stick a fibre optic camera down your manhole cover to find out what the blockage is.....oooh yeah, its gonna need a high powered waterjet down there...that's gonna cost ya" that watchdog and the likes featured not too long ago when really it could have been fixed in about ten minutes

cheers

 

[felix]

You should definitely listen to those alarm bells. So "your radiators are blocked" are they? Then how are they getting hot? Did he put a few kilograms of plutonium in each one? I very much doubt it. This geezer is clearly talking total b****x so I wouldn't trust him to fit a three port valve properly either. Unfortunately there are many wrong ways in which you can fit a three port valve so you'll either have to learn how they work or get a different plumber in. Given that the next plumber might not be any better, read on.

Three Port Valves for Dummies:

There are a few minor variations but all the three ports I've ever fixed worked in much the same way.

1) The valve rests in the HW only position. The HW demand from the controller switches only the boiler and pump. The tank stat can over-ride the controller and turn that HW demand into a No-HW demand.

2) A CH demand from the controller and room stat goes to the valve motor and drives it to the mid position. At this point a microswitch in the valve head cuts the motor power except for a trickle of current through a resistor; just enough to hold the valve against the return spring. The boiler and pump are already on because of the HW demand.

3) What happens when the demand is for CH only? Well, that microswitch is a change-over type and the motor is now connected to No-HW from the controller. No-HW is a real wire, not just an absence of HW demand. IF AND ONLY IF the motor has already reached mid position, the No-HW demand will drive it on to its end stop, closing the HW flow. But surely the boiler and pump are off? Here comes the clever bit. When the valve reaches the end stop a second microswitch connects the CH demand wire to a third wire going back to the contoller's HW demand terminal. This back feed of power now controls the boiler and pump. On old fashioned electromechanical controllers it will also switch the HW light on which can be a bit puzzling. The valve will stay in the CH position for as long as No-HW is live.

If you can get your head around all of this you can start fault finding your new valve. The first thing to check is that the thing is fitted the right way round. If that doesn't fix it you'll have to check out the voltages on its wires under various controller/stat conditions. Apart from the three already mentioned, there will be a neutral wire and, possibly, an earth. Good luck.

PS: There should be a manual over-ride lever on the valve head. This allows you to open the valve to mid position for filling and bleeding purposes. It is also useful for fault finding.

 

[doitall]

what model netaheat.

the divertor valve can you say what pipe goes to the cylinder, there will be an A or B on the valve body.

Problem sounds like air in the primaries, so is there an ait vent on the cylinder, and if so turn the cylider stat off and the heating on then bleed it of air

 

[ChrisR]

A way how the guy might be right is that corrosion which produces sludge(and may well be the uneven rad temp cause) also causes gassing, which can stop circulation. Have you checked the air vent by the HW cylinder, because if that loop fill with air you get your symptoms exactly.

I find it difficult to replace a valve head wrongly cos they only fit one way. If you latch the lever onto the "Man" position your water should get hot when the boiler's on.

I have fitted 3 port completely the wrong way round, so the HW heats up only if the rooms are too cool.... Temporary get-by for that was to take the head off and put the valve in a mostly-heating position!

 

[felix]

Doitall has just mentioned something I omitted, namely bleeding air from the cylinder heating coil. I assumed you would have done this because you talked about bleeding everything - but that was BEFORE Mr Powerflush arrived! It's a very simple thing to do so take Doitall's advice and look for a bleed valve near your cylinder.

 

[daved]

Gents,

Thanks for the info, I have an update

The air vent by the hw cylinder was bled, air came out, but the HW still didnt heat up.

I called another plumbing company out and he checked the system. You'll have to bear with me here as my plumbing jargon isnt the best but basically he said the the water in the cylinder (which up until now i'd called a tank!) wasnt heating up because the tap valve that comes off the pipe at the bottom of the cylinder was faulty and the gate was stuck in the shut position (if that makes sense !)

he was at a loss to explain why this meant no CH, other than saying that they may have taken the return from the same pipe that was cold because of the gate being shut.

They're coming to fit a new tap valve next Wednesday. He said if this doesnt cure the CH as well as the HW then i'll need to flush the system.