central heating only comes on with h water, stumped engineer

[doitall]

We're not forgetting that everything electrically works as it should. because I don't think it does.

Maybe a system and electrical fault or either.

Also remember the primary pipes were gravity, they would still circulate if there's an open circuit.

Has any one check the MV is the right way round.

 

[Mikefromlondon]

Ha ha quite an intersting thread, evryone is bangging their heads! I feel I could also bang mine!

when you have a problem on a fairly complex system, it is better to isolate the problem into smaller sections, taking one section at a time, applying logical thinking, one can sort all kinds of hurdles.

But this requires patient and logical thinking.

One also has to have a fairly good knowledge of how central heating systems work, that is important of course. Knowledge about how motorsied valves work, 2 way valves, 3 way valves, spring return etc, with or without manual override.

Don't forget to rule out the programmer and the timer switch, most faults can be due to this controller not opening valves when it should due to poor contacts etc on the slider switches.

And fully understand all pipework, lnstallation layout type, identify correctly all pipes, all valves etc etc. Its easier said than done as some of the pipes are run behind things and underfloor, so it can be quiate a painfull diagnostics!

Motorised valves, if wired incorrectly can lead to all sorts of problems, valves that are suppose to be closed are open and those which should be open are closed due to erronous wiring.

So the first thing to do would be to isolate all motorised valves, remove the actuators and manually throw the system into either HW position and see if the boiler runs perfectly well without over heat tripping on the boiler, feel the heat travelling into the pipes as they get hotter, as expecetd when the boiler has fired up, have the HW storage cylinder thermostate in place and make sure you test it by turning its pot to a lower temperature setting to check boiler stops heating any further hot water, when satisfied, turn it up to its normal temp. But it must be turned up first or the boiler may not fire at all if the water in the cylinder is already too hot.

Same way, now manually turn all the valevs to CH mode, you have to be sure which way does a valve close or opens and a 3 way valve would work both ways as well, so as you test your hot water, this time you test your CH, and if this way you don't get any problems, you know you can almost say there is a wiring issue as some of the valves may be operating incorrectly.

having said all this, ensure that there isn't anything obvious wrong with your boiler to start with, and that your pump functions as it should, no air trapped in the system anywhere, all rads are clean and all rad valves are free to circulate.

This sort of problem is beyond many service engineers, as first of all they haven't got the time and you haven't got the money to pay for a possible full day diagnostic, most would want to come and leave as soon as possible as there are other jobs pending, having said all this, it is with no disrespect to any engineers on here.

 

[bonkersbill]

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I will work my way through each recent post as quick as i can

 

[bonkersbill]

Hi Mike, just run your tests, removed actuator and turned valve manually to HW only, turned on HW & CH at programer and boiler starts, turned tank thermo down, boiler shuts of, turned thermo back to 60 deg and nothing happened, turned it up to 90 and 2 mins later boiler started up, turned it back to 60 and 2 mins later it shut down and did not come back on after 10 mins, turned it back to 90 and 5 mins later it fired up and stayed on for 2 mins.
i reset the programer and tried to do the same in CH only position with CH & HW on at programer but the boiler still shuts of after timed 22 seconds

 

[UpgradeME]

I will work my way through each recent post as quick as i can

A quick observation and something worth double-checking:

The installation manual shows the boiler's flow is at the top & return at the bottom. If that is the case, the pump will be pumping the RETURN which will work okay when the 3PV is set for HW (Port B) but may have restricted FLOW feed when set to CH (Port A) and cause your symptoms!

Can you check the direction of the arrow on the pump and if the pipe at the bottom of your HW tank is hotter than the one coming out half way up when HW is being heated? If so, it may explain what's happening with your system (reverse flow) and someone more experienced in plumbing can advise you how best / easiest way to correct it!

If the flow is the correct way, I would say 4xpaws suggestion of the CH return being tapped into the flow feed sounds fesible (i.e. the horizontal pipe in your drawing closest to the boiler) - This may not be the 'correct' method, however, as a simple test I would try fitting a temporary return (for test purposes) from perhaps a radiator drain valve to the HW tank drain valve (assuming there is one for the CH side, NOT DHW) thus creating a return route from the CH circuit via the HW return. If that worked, I would have more confidence removing floorboards or panels to try & find where the CH return Tee's in and correct it.

 

[Mikefromlondon]

Hi Mike, just run your tests, removed actuator and turned valve manually to HW only, turned on HW & CH at programer and boiler starts, turned tank thermo down, boiler shuts of, turned thermo back to 60 deg and nothing happened, turned it up to 90 and 2 mins later boiler started up, turned it back to 60 and 2 mins later it shut down and did not come back on after 10 mins, turned it back to 90 and 5 mins later it fired up and stayed on for 2 mins.
i reset the programer and tried to do the same in CH only position with CH & HW on at programer but the boiler still shuts of after timed 22 seconds

those delays are expected and normal due to hystresis in thermostates, and also the new settings will take a while to reach thermal equlibrum, so thats fine, like wise you did the CH, and there is a problem here obviously,

while doing the above, did you confirm the position of the valves spindle in relation to where the motorised valves are parked in HW state and in CH state, if they correspond to the correct positions, then you obviously have a flow problem in your CH circuit, and as per other posts on here suggesting you to check your flow and return look for blockages, the blockage is likely to be in the main feed out from the diverter valve, but I can't see it being on the return path as that would have also stopped your HW heating and overheat your boiler. And it is unlikely any blockage was within an individual radiator only that rad would not be heating up., so its time to open up some valves physically by draining out your water, and check for any obstruction in the valve ports or pipework. after of course checking what the above post from upgrademe has said to check.

 

[bonkersbill]

Hi Dave i will try to answer all your questions but please bare in mind i am not a proffessional and am doing my best with observations

3, further to my earlier post: The pipe in photo 1 marked "22to28 to boiler"
this pipe has 2 ends
end 1 is connected to? Wrongly labled but does go to rads under the floor
end 2 is connected to? bottom of 3pv

4, pipe from bottom of 3port valve goes to?
This is the 22mm one that has a bend at the bottom and eventually goes under the floor to feed the rads
a, is it joined to pipe marked "22to28 to boiler"?
it is the same pipe and i have marked it wrongly, it does not go to the boiler, it does pass directly under a pipe which comes out of the bottom left of the tank which is 22to 28 to boiler
b, does it go through floorboard DIRECTLY below 3pv
No, it is bent and goes 1.5m before going through the floor to rads
c, if none of the above where does it go?

d, is photo of the under floor pipework DIRECTLY under the 3pv.
no 1.5m away
e, in above photo does the pipe go DIRECTLY to the 3pv
yes with a couple of bends
f, in the picture of the 3pv the pipe leaving the bottom of the 3pv showes it going into a fitting of some sort, what is this fitting?
this is an on off tap
g, if a Tee where do the other two pipes go to?
A bend to under floor
Read more: //www.diynot.com/forums/plumbi...-stumped-engineer.295212/page-9#ixzz1ngBvctbL

 

[stardanny]

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I will work my way through each recent post as quick as i can

It look like it used to be gravity hot water and pumped heating and been changed to fully pumped "y" plan system using 28mm pipework for flow to airing cupboard and another 28mm return from cylinder back to boiler, that work perfect. However the flow from 3pv to radiator, with full flow when hot water port closed, the return from radiators cannot cope with full flow rate back to boiler, boiler keep cut out.

Where the return pipe from radiators to tee into 28mm return that is also from cylinder return, that might be where the problem is. It may be unsized, near blocked, possible a injecter. a photo of inside duct showing the pipework would be better.

The pump, by looking at photos, is the right way, pumping toward 3pv.

Dan.

 

[bonkersbill]

Hi Doitall, i dont know what MV stands for.
Mike how do i find the diverter valve
Upgrademe, i'm going to check now

 

[doitall]

MV is motorized valve.

Good first post Mike, but not sure what your saying in the next.

if they correspond to the correct positions, then you obviously have a flow problem in your CH circuit, and as per other posts on here suggesting you to check your flow and return look for blockages, the blockage is likely to be in the main feed out from the diverter valve or on the return path, since if the blockage was within an individual radiator only that rad would not be heating up., so its time to open up some valves physically by draining out your water, and check for any obstruction in the valve ports or pipework

Lateral thinking.

If there's a blockage the rads will not get hot.

Assuming the drawing is reasonably accurate I don't like the heating return.

Do you know whether it used to be or may still be a one pipe system. In which case has TRV's been added.

 

[Mikefromlondon]

Hi Doitall, i dont know what MV stands for.
Mike how do i find the diverter valve
Upgrademe, i'm going to check now

A diverter valve is a 3 way valve in your installation, usually sited near the hot water cylinder, hot water from the boiler is pumped into the middle port,
then the motorsied valve diverts it to either CH or HW ports or Both in the case of a 3 way valve, so it has 1 inlet and 2 outlets, one outlet feeds the Hot water cylinder Heating coil, the other port leads the hot water from the boiler to CH circuit.

But when you require both CH & HW, this diverter valve can hang midway and supply to both circuits.

Since you are getting some heating in your rads when you put your system in both modes, i.e. CH & HW, it then happily heats your CH radiators, but not quite, as you said they don't heat up well.

I didn't think they would heat up well, simply because, you have some partial restriction, which when you are in CH mode only does not allow sufficient flow through your CH circuit so overheats the boiler which cuts out, but in dual mode (CH+HW) it does not cut out and heats up the rads as some flow even though much restricted does flow through the rads or the CH circuit.

in HW mode, there appears to be no blockages or restrictions, so it flows happily, and the boiler does not shut down due to overheat. But I am not sure if it would shut down when your hot water thermostate has reached the desired temeprature, then the diverter valev would change and divert all the hot water from the boiler to CH, in which case your boiler would shut down due to flow restriction, when it is in both CH+HW mode, again depending on the thermostate settings in room and on the cylinder.

So in my view your problkem appwears to be associated very close to this 3 way valve, on the port that feeds CH flow, but not return,however, there can be a problem in the return too, I am not ruling that out. But I would check this 3 way valve ports and the CH circuits are all clear of any obstruction, have all your rad valves fully open.

 

[bonkersbill]

Got confused with changes to terminology, i assume
MV = actuator
Diverter =3 port valve, 3pv
i've replaced both the actuator and the 3pv with no change.
i cant see an arrow on the pump but someone has posted it is the right way round.
i will have to come back to testing which pipe from the tank is the hottest because they are both red hot, i will test from cold but i think i have already done this test with the 28mm pipes to make sure it was pumping in the correct direction, i will check again.
Mike, when i've open all the rads to full (i only have 1 that is open partially, the rest are open fully anyway) what am i looking for

 

[stardanny]

Can you access to duct by the side of chimney? I'm sure there should be a access panel for draining down of system near the boiler.

Dan.

 

[Mikefromlondon]

Got confused with changes to terminology, i assume
MV = actuator
Diverter =3 port valve, 3pv
i've replaced both the actuator and the 3pv with no change.
i cant see an arrow on the pump but someone has posted it is the right way round.
i will have to come back to testing which pipe from the tank is the hottest because they are both red hot, i will test from cold but i think i have already done this test with the 28mm pipes to make sure it was pumping in the correct direction, i will check again.
Mike, when i've open all the rads to full (i only have 1 that is open partially, the rest are open fully anyway) what am i looking for

Oh I said make sure all your rad valves are fully open to start with, to rule out any possibility of flow restriction in the CH mode. thats all.

I got a feeling you got something stuck in your diverter valve port to CH, did you have the whole valve changed? or just the actuator?

 

[doitall]

The Port B on the MV should go to the cylinder.

There's an arrow on the back of the pump casing.

Do the rads get hot or not, I'm not concerned whether some get hotter that others or not as that could be a case of balancing.

How accurate do you think the drawing showing the heating pipework is.

And have TRV's been added.