CH temper mental

[Mr. Tickle]

Hello everyone!

We've moved into a new house with a HW/CH system - boiler, hot water storage tank, T-valve thingy, thermostat in living room, therm on tank, cold water storage in loft, electronic programmer (danfoss CP15)

I have no idea what the technical terms are.

Most times everything works without a problem. Sometimes, however, I'll come in after work and turn the therm up, which will kick in the boiler - but it will get warm and then cool down within about 30mins.

When this happens, The therm in the living room is calling for heat, the programmer says it's on, the pump is going, the boiler is on and everything seems to be the same as it was when it is working - only the rads are cold/barely warm.

Sometimes when this problem arises, i'll go to the valve and pull the lever across. I'll hear gushing of water then the pipes leading to the rads will get hot, but this doesn't always happen. Sometimes the lever will already be on MANUAL and it's just floating freely. If you move it, nothing happens.

Is there a flow chart of things to check, to make sure everything is working?

Does anyone have any idea what is going on?

Could it be the programmer? Even if it says it's calling for heat, might it not be?

We've had a plumber come in and he just want to replace each part and see if it works. He said he couldn't fix it 'cause when he came round, it was working. He seemed to think we were lying or being funny when we described what was happening.

It seems to happen more on the weekend, when we want heat all day.

Any help anyone can give would be greatly appreciated. If you can point me in the direction of a good book or website that has a troubleshooting guide in it, that would be good.

Many thanks to anyone that responds!

Mr. Tickle.

 

[croydoncorgi]

There's no flowchart as such - but there is a 'chain of command ' that already points to your problem cause.

The key sequence is Programmer - Thermostat(s) - Zone / 3-port valve(s) - Boiler + Pump.

(In some cases, the pump and boiler are wired in parallel. Most modern boilers include 'pump overrun', in which case the valves fire the boiler and the boiler powers the pump.)

If something towards the Left of the list fails to work, then nothing to its Right CAN work!

The other thing to remember is that large things like pumps, boilers and programmers DO fail but wiring hardly ever does 'by itself'. So if SOME bits of the system are working, perhaps some of the time, the key things to look at are the controls.

If the programmer appears normal (indicator lights, display, clock dial going round, ...) then it's probably working.

If the wall and cylinder thermostats make an audible 'click' when you turn the dial, then they're probably OK too. (But note that some electronic thermostats do NOT click at all, or only click when they are receiving power.)

If moving the 'manual' lever on a 3-port or zone valve creates some activity (boiler firing, pump running) then chances are that the valve was stuck and you just freed it. Note also that in the case of Honeywell valves, manual operation CANNOT(by design) operate some or all of the electrical switches inside the valve, so you CANNOT push the lever across to fire up the system. If the valve WAS stuck, then it will soon stick again. Don't just get back under the duvet!

In your case, my best guess is that your 3-port valve is partly stuck and is operating mechanically but not electrically. As a result, your rads WILL come on but only when the system is ALSO heating the hot water. Simple check to prove this: turn on CH AND HW, wait until rads start to warm up, then turn off the hot water switch on the programmer. If pump and boiler switch off, it's 95 percent pointing at the 3-port valve.

 

[Mr. Tickle]

Brilliant, that's just brilliant. Thanks for your advice - i will have a play around tonight when i get back from work.

The three port valve - this is the white block thing, yes? It has one pipe going to HW to the left, one to the right going to CH and the other comes out the bottom and comes from the system.

The valve - should it have three positions? I can only see MAN and AUTO on the top of the lever. Everythin i read about 3PV says they have three settings.

A plumber said something about not being able to have both hot water and heating, or the other way round. He said it was something to do with the way it was setup. Does he mean the controller is that way and we could just get another or does the physical arrangement of the plumbing prohibit this?

The thermos do click - they are all bimetal strips as far as i can tell.

The valve does move if you change the thermo on the tank.

Anyway, i'll have a play around tonight as I said and get back here later on or tomorrow.

Thanks again for your input.

 

[croydoncorgi]

As I said, 3-port and zone valves are not intended to be operated manually. The manual position should be used (only) to allow water to get past the valve when the system is being filled up. This said, it IS possible to wedge open a valve and rewire other bits so the HW and / or CH work 'a bit' until the valve can be changed or repaired. But it's a bodge.

There are also various types and makes of 3-port valve. Some are 'hot water preference', in which case the valve's 'rest position' is with the path to the CH closed. Others are 'mid-position', so that both paths are half-open until the valve is driven one way or the other. Yet others motor round CH - both - HW - CH and if they fail, stay stuck in the last position. Not straightforward.

 

[Mr. Tickle]

Wow, ok. So do i need to find the model number to find out exactly which one it is - would that help diagnose the problem?

I presume i need to call a plumber to come in and swap over the valve? Is this a big job, any idea on the length of time something like this should take?

I will have a look tonight and write down as much as i can.

Thanks again.

Mr. T

 

[keego]

It realy depends on the make of the valve as to wether it's easy to repair, some you can remove the head & change it, others it's a drain down. If you can change the head then it's just a matter of a few screws & wire like for like in the 10 way box.

 

[felix]

All the three port valves I've ever looked at work in much the same way.

1) They rest in the HW only position. An HW command from the controller powers the boiler/pump.

2) When you demand CH as well as HW, the CH demand drives the valve to mid position. The HW demand still powers the boiler/pump.

3) When the hot water is hot enough, your tank stat will turn any HW demand into No-HW, regardless of what the controller says. No-HW drives the valve all the way over. Until it gets there the boiler is OFF because HW has gone.

4) When AND ONLY WHEN the valve reaches the CH only position, an internal microswitch routes power from the valve BACK to HW demand on the controller. This backfeed of power restarts the boiler/pump.

From this you can see that if that switch fails you will not be able to get CH on its own. Once the water is up to temperature your heating can't work. Does this theory fit your symptoms?

 

[Mr. Tickle]

What you are saying makes sense to me, yes. So thank you for the explanation. Everything seems to work as you are saying. Right now - the tank has just clicked off, it's hot enough. The Controller is calling for CH and so is the Thermostat in the living room. The Valve is floating freely in that I can move it without resistance. The Pump is going and the Boiler is on, but the water going round the system just isn't hot.

This is where i can't see the problem.

We don't use the programmer 'cause of these problems, it seemed to work when we just used the Thermostat to turn the system on or off. So i come in from work and turn it on and it gets hot for an hour. Then the whole thing is just cooling down.

I once stood on our kitchen worktop and felt the pipes coming in and out of the boiler - neither of them was hot. Surely at least one should be hot?

But then if it was the boiler, it wouldn't work at all, or would it?

I'm at home now and have just noticed that the rads were cooling down and for the life of me can't see why. Again!

Thanks again for any help - i'm really up for learning how this whole thing works so i can solve other problems in the future.

Mr. T.

 

[Mr. Tickle]

OK, i've just put the CH + HW on manually using the programmer. I turned the therm on the hot tank up and it clicked on; the valve moved into mid position and i can hear a gushing of water.

So i'll see if it heats up. Every switch and valve seem to be working.

If it does, i'll turn the HW off and see what happens. Should i stop the HW at the programmer or by using the therm on the HW tank?

Cheers!

Mr. Tickle.

 

[ChrisR]

It shouldn't matter, they're switches in series so if one's off it's off.

Yer valve. If it's white (not metal topped) it's probably a Potterton,Myson, Danfoss, Sunvic ... They mostly work as felix said - though some motor open and motor shut. But it sounds like you have the ordinary type. When the lever is in the resting position (you can push it against the spring) that's HW only. If it goes to the middle position, HW + CH, the lever will be floppy/no resisitance, as it would be in CH only which is further round.

Next time you catch it not working, try undoing one of the two(probably!) screws you can see which holds the white bit of the valve onto the brass bit. Good chance that if the valve's stuck, one turn undone and it'll free. Mine worked 5 years like that.

Just one other check - when it's gone off (and you reckon it should be on) try bringing the HW on. if that brings the CH on too (just feel the pipes) then it's deffo the valve head faulty.

The wiring diagram is here, if you feel curious.
http://content.honeywell.com/uk/homes/Catalogue/Sundial Plans/3.4 Y Plan.pdf
If the head is faulty, it's likely to be one of the microswitches inside, which are a bit of a pain to change, so you'll need a new head (number will be on its bottom.

 

[Mr. Tickle]

Ok, so nothing has got hot. Everything is just warm. I think the hot water tank is keeping the rads warm 'cause the tank temperature has dropped by 10 degs.

I have clicked the hot water tank therm off, so it has stopped calling for hot water - and the valve moves over. The water isn't hot though - it is still pumping round and is just warm. The boiler is still on and the thermostat in the living room is still calling for heat. The programmer is still calling for HW + CH.

What do you think?

 

[ChrisR]

'Bout time we knew what your boiler is.

If it's pumping water round the rads then it isn't a faulty valve, it points to (the hysteresis of ) the boiler thermostat being too wide. Try turning the boiler temp up.

 

[Mr. Tickle]

The boiler is has high as it will go. Last night it worked perfectly with the rads bouncing off the walls.

It is a Gloworm model, but i haven't been able to locate a more specific number yet. I will have a look again in a sec.

Why do you think it would work last night and now it's duffed?

Mr. T.

 

[Mr. Tickle]

OK!

It's a Gloworm Ultimate 30FF.

Does that help?

Mr. T.

 

[Mr. Tickle]

Okay, we turned everything off because it wasn't working and have just turned it back on. The rads are bouncing off the walls but everything is exactly the same as it was when we turned it off.

What is going on?!?