CH temper mental

[felix]

That's what I'd like to know! You reckon your boiler and pump are both running and yet the water in the pipes is cool. Sorry but your system can't defy the first law of thermodynamics. Something is not happening in quite the way you think. Check this:

With CH only on demand (which you know doesn't work) does the boiler cycle on and off; mostly off? This means that the water isn't getting to the radiators. It's running round some short bypass loop and returning almost as hot as it went out. Maybe it never even gets out of the boiler! In these circumstances the boiler will go on and off on its own internal thermostat.

With HW only on demand, do the radiators get hot anyway? If they do then I can suggest a possible answer to this puzzle - the pipe leading out from the CH side of the three port valve is blocked.

Now how, I hear you ask, can the radiators get hot at all if their feed pipe is blocked? Here's how. With the HW flow open, hot water returning from the cylinder coil does not take the obvious route back to the boier, at least not all of it does. Due to poor pipe layout it shoots straight into the return pipe for the radiators on one floor and goes round these ones backwards. It arrives at the valve CH outlet which is closed/blocked and goes the correct way round the radiators on the other floor before finally returning to the boiler. I know this can happen because it happened to me!

 

[Mr. Tickle]

Okay, the only thing that we can work out as having some sort of pattern is that the heating turns off after the water goes off - only the CH doesn't come back on - it just gets cold.

Is there anyone that can make head or tale of this?

Thanks for anyone who can help.

Mr. Tickle

 

[ChrisR]

Felix what you describe can only happen if the return pipes aren't all taken back to the boiler. Then it can happen without blockages.

Mr T, your boiler will be on and heating as long as the switched live going to it is mains voltage. Measure it. The switch in the 3 way valve should be sending mains to the Sw L. If that line is live the only thing which can turn the boiler OFF is its own internal thermostat. It's just possible that the voltage isn't proper mains sometimes so the boiler does funny things. Have seen it just once, check it.

But the behavious you describe last is what you might expect if the 3 way V isn't working properly. The heating goes off after the water goes off. That's because it's the water thermostat which was holding the boiler on. Look at the wiring diagram and you'll see it. When that goes off the live to the boiler is supposed to come from the switch in the 3 port when it's made, when the valve moves across. But if it doesn't move across quite far enough or the switch inside is dud, the valve opens but your boiler goes off.

 

[Mr. Tickle]

ok. thanks for the input. This is much appreciated.

CroydonCorgi - The programmer appears normal, yes. The Thermostats appear normal and to my observations work to call for the correct things from the programmer.

It is happening again tonight - so i have put the prog. on to call for HW + CH, but there isn't much going on heat wise. The boilers on, pumps going and the valve has moved over to the middle (slack towards the auto position and sprung towards the man. side.). How long should it take to get hot?

I have felt the pipes on top of the boiler and they are both warmish. One appears slightly warmer than the other. Should one be untouchably hot? I presume so as the radiators were that hot when I came in from work today.

If someone could let me know how long it should take to heat up, that would be great.

I am now calling for HW+CH with all the Therms on, prog on, valve in mid position and it all seems to be working in the same way that it does when the rads are hot, but it aint hot yet.

ChrisR - The valve is a Danfoss white plastic cap model with two screws on opposing corners. I can just take these off without any problems?

I don't know what it's resting position is; but it is in the middle with HW+CH being called for at the moment.

It is sprung towards the side that says MAN and floppy towards the AUTO side. When it is calling for just CH, it is floppy across the scale.

I am doing as you suggest - calling for HW+CH now it has gone cold. The valve moved okay to the mid position and I'm gonna wait for the rads to get hot. I have explained above what is currently happening.

Felix - thermodynamics - well, i guess that's why i'm here. I can't figure it either. With CH only on, the boiler does not cycle on/off at all.

With HW only on, I do not know if they get hot - i will find out later on as i am going to try the HW+CH thing first. I will update tonight.

Again, thanks for your input. It's not something i really understand and i can't find any logic to this at the moment!

Cheers,

Mr. Tickle.

 

[Mr. Tickle]

Okay, it's been about an hour and the house is getting colder. No action with HW + CH on, although everything looks ok.


I am now going to ask for just hot water and see what happens.

I have done this by turning the room therm down, although the prog is still ON for CH, the therm isn't calling for it. The boiler continued and the valve has now moved all the way over to AUTO, It is sprung to the MAN side and difficult to move. The water seems to be moving through the heat exchanger (the coil in the tank) but I can't feel much heat.

It is warm but not that hot. I think that the heat in the HW tank is heating the pipes - could this be correct?

Mr. T.

 

[Mr. Tickle]

Ok.

The rads are not hot with just HW on. There is not hot water in the pipework.

I have just turned the hot water therm down and the valve moved over, the boiler went off. No therm was calling for heat so the valve returned - i heard a microswitch click as it moved across.

I turned the room thermostat up and the boiler has fired up again, pump is going and the valve is slack over the MAN AUTO scale.

I will see if the rads get hot, but i don't think they will.

Can anyone see any reason for it not to be working, with the above as I have described?

Thanks again for any help you can offer.

Mr. Tickle.

 

[felix]

Your last post has, without you knowing it, described a perfectly functioning valve. When you call for CH only, the valve moves right over (as indicated by the lever going slack), a switch clicks and the boiler starts up.

Here's the thermodynamic problem. With your boiler apparently on and not cycling, there should be lots of heat coming out of it and this is what you don't have. I'm beginning to think that your boiler isn't getting very much gas. One way to find out is to watch your gas meter.

A cubic foot of gas is roughly 1000 btu; that's 300 watt/hours in new money. An average sized boiler should be eating up about a cubic foot every minute. What's yours doing?

 

[ChrisR]

I'm also wondering if the head of the valve is doing its thing but the wet bit isn't.
Yes you can unscrew the two corner screws and take the head off. The operating part will either be a D shape or a thinnish rectangle, and there will be a type number on the underside of the head. HSA3 , 5651, 2701 or something. What is it?
Its sounding like the parts which divert the water are mostly sending it to the HW cylinder, and rarely/never sending it to the CH.

You should be able to move the bit sticking up from the brassy base; see how it feels. I think I've got every valve yours is likely to be so I can compare.

 

[Mr. Tickle]

I will have a look at the meter tonight.

Would this explain why it worked sometimes, but in the afternoon and on weekends, it seems to fail?

Mr. T.

 

[felix]

ChrisR has already mentioned one possibilty though I've never seen it happen myself. If you aren't getting the full mains voltage to the boiler, the gas valve might not open properly. If you do find that the gas flow rate is too low, this is the next thing to check.

 

[Mr. Tickle]

WIll check tonight - what if it is okay though? What else could it be?

How long should the system take to heat up?

If the boiler is on and running, should one of the two pipes in the top be very hot?

Mr. Tickle

 

[ChrisR]

Certanly the boiler flow pipe should get hot pdq. You'd expect one rad to start feeling hot at the top edge within a minute ar two, and all of them getting hot after say 5-10 mintes.

Seems a daft question, but when you say the boiler's ON, how do you tell? Light on the front, or looking at the flames...?

Another obvious thing to do is feel the pipes right at the diverter valve. The middle one should be hot quickly, and the "active" outlet pipe should be obvious too, though after a short while the non-active one gets warm, by conduction.

You might have a sticky gas valve - many start at a low pressure then ramp it up. If stuck on low sometimes...

 

[PTH]

Are you SURE that the pump is running rather than just making a noise and vibrating?

 

[felix]

Fair question PTH. It certainly wouldn't help to have a jammed pump. The HW circuit might work, if rather badly, on gravity. On the other hand I don't think a bad pump can explain how the boiler 'runs' continuously without anything getting more than warm. Particle pair production aside, you cannot simply lose energy. If it isn't coming out then it's not going in.

 

[PTH]

Well, if the pipes out of the boiler are not getting hot, the boiler isn't firing.

Even if the pump is stopped the boiler may fire until high temperature lockout caused by low flow.

Early on in this thread there was a mention of gurgling air/water noise followed by the rads warming up; in my experience that only happens when a pump starts or if there is a lot of air in the system and a valve is opened.

What I am trying to establish is whether there is any flow in the system (pump failure/air lock) or the boiler just isn't lighting up (gas valve as pointed out by ChrisR).