Central heating pump and boiler

[John.g]

Quite possible but why isn't the circ pump running during this random period.

This link is excellent but it takes me a long time to absorb it each time I look at it.

Y Plan central heating system

Y-plan central heating system operation and wiring diagram

www.flameport.com

 

[exedon2]

True enough boiler and pump should be linked unable to run independently

 

[nut&bolts]

Quite possible but why isn't the circ pump running during this random period.

The pump only runs when mannualy switch on through controld or it is on timer. In my system it never was running when controls were off.

Interestingly, the central heating works okay. when I switch it off from thermostat or controls, It goes off but hot water keeps getting hot and hotter
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To clarify, when I switch on central heating or hot water to get heated in the cylinder, then only the pump and boiler runs. When the controls are off, the pump does not switches on, despite boiler coming on randomly

 

[John.g]

Have to sleep on it tonight.
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Just a few more comments.
You confirm that system works in all three modes, ie, CH only, HW only, and CH&HW.
Also that when you have CH only selected and it switches off then the boiler (only) will fire randomly but heats the HW cylinder.
The valve is supposed to stay in the last selected mode (except if whole system is powered off where it will revert to HW only) so this doesn't seem to be happening as the random boiler firing is heating the cylinder and should be trying to heat the rads if CH only had been selected.
The only suggestion I can make just now is to shut off the power then remove the orange wire temporarily then restore power and with both CH and HW off see if the boiler still randomly fires.

There was a problem some years ago with the UPS2 pumps which was was damaging contacts etc but I think was solved by supplying a suppressed pump cable but as your pump is new then can't see this as causing the problem.

 

[SJB060685]

I have read all comments but forgive me if I've missed something.
The wiring on these systems is simple, by no means as complicated as some modern systems.
By the sounds of it something is not wired up right.
When the room stat or cylinder stat calls for heat the motorised valve does its thing internally and the boiler and pump are brought on. Both lives to each are tapped into the connector with the orange wire from the three port.
Another possibility no one has mentioned but I doubt is the case is is there a frost stat somewhere?
When wired correctly the boiler and pump should only be energised when theres a demand and it comes from a switch live, there should no link to any other live at all.

 

[nut&bolts]

I have lived in the house for few years and always either hot water has worked or the central heating. They don't work together.

I changed the thermostat on the water cylinder this morning and problem is still the same.

I called a plumber, he checked the thermostat in the boiler by measuring temperatures (cuts off at 60 and comes back around 45 C) and thinks it is working fine.

He wasn't fully sure of three port valve... He measured temperatures on central heating pipes and hot water pipes whilst switching controls on and off. He couldn't say whether it was broken.

He measured the emissions (CO) and said that they are high and need to replace the boiler 🙁

I am now lost. For me, apart from hot water getting excessive hot there isn't another problem.....

 

[Ben-gee]

Is immersion heater on?

 

[SJB060685]

As I was suspicious of. You say prior to commencing the works you only had HW or CH, not both? That would imply you have a three port diverter valve.

 

[nut&bolts]

Yes that correct....this is how it has always been.
No there is no immersion heater in the cylinder
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Yes three port valve is there

 

[SJB060685]

Ok. When you replaced the pump was all you did was just swap the pump cable and wires out?
Where is the boiler situated?
If you take the cover off the wiring centre how many wires were going to the boiler?
As I said the boiler should only be energised at the same time as the pump, unless of course, as mentioned above its getting a feed from elsewhere.

 

[John.g]

As I was suspicious of. You say prior to commencing the works you only had HW or CH, not both? That would imply you have a three port diverter valve.

Have you a wiring diagram SJB for this type of diverter valve. Of course the existing one might be a mid position valve and just not working in mid position for whatever reason.
The frost stat did cross my mind also but the big mystery is why the circ pump doesn't run with the random boiler run.

 

[SJB060685]

Have you a wiring diagram SJB for this type of diverter valve.
The frost stat did cross my mind also but the big mystery is why the circ pump doesn't run with the random boiler run.

This is what’s called a W plan mate, not the Y plan. It gives HW priority, meaning once CH is satisfied it will spring return to HW port. Of course if the boiler is getting a feed from somewhere other than intended then through gravity circulation the cylinder will continue to heat until boiler water and cylinder temperature reach thermal equilibrium but you know that already.
It is a Honeywell wiring diagram but this is the principle behind the diverter.

 

[nut&bolts]

Guys , thank you so much for advices.

What shall I do first to strat with ? Change the boiler as plumber said or try to fix the current problem and how?

 

[SJB060685]

Guys , thank you so much for advices.

What shall I do first to strat with ? Change the boiler as plumber said or try to fix the current problem and how?

The boiler has to run through a signal from somewhere. Im not convinced you need a new boiler but it does require someone to test the wiring.

 

[nut&bolts]

Is it possible that wiring faults develops after a while?. Previously it was fine.

Also why is plumber suggest to change the boiler bxoz of increased emmissions.wht is the risk. Is it dangerous etc?

 

[SJB060685]

To answer your first question. Yes electrical faults can occur at any time, they can also coincide coincidentally with other work undertaken. Having said that boilers don't just magically ignite it takes a series of commands starting with a demand electrically.
Question 2. I imagine the plumber who attended just checked the ratios. He is right that high CO readings are potentially dangerous, carbon monoxide is a silent, odorless and tasteless killer, it only takes a small ppm number to be affected, however a good engineer can keep a boiler running safely, which ALWAYS comes first and operating properly thereafter, providing parts are still available. I cant say too much about gas as I'm not qualified but I am an oil man and know that not only is carbon monoxide a by product of burning hydrocarbons, it can also be controlled if someone knows what they're doing and again parts are available. I suspect and I could be wrong he was just pushing for a new install and to be fair your boiler is getting on a bit.

 

[John.g]

This is what’s called a W plan mate, not the Y plan. It gives HW priority, meaning once CH is satisfied it will spring return to HW port. Of course if the boiler is getting a feed from somewhere other than intended then through gravity circulation the cylinder will continue to heat until boiler water and cylinder temperature reach thermal equilibrium but you know that already.
It is a Honeywell wiring diagram but this is the principle behind the diverter.View attachment 45876

The W plan diverter valve wiring is quite easy to understand but SJB or someone might comment on the wiring if pump overrun is fitted.
referring to the boiler terminal box, assuming L is taken from terminal 7 and assuming a call for CH or HW then L will be live and the boiler PCB should then energise PL ,pump Live, and keep it running continuously until terminal 7 is de energised. L should also enable the boiler to run continuously also unless its minimum output exceeds the heat demand, at which point it will cycle on/off, again until terminal 7 is de energised.
When terminal 7 is de energised (no call for CH or HW) and if the pump overrun is initiated via terminal 10 then SL should tell the PCB to energise PL only and run it for the overrun time. If what I have written is basically correct then can some one see how this could have been (mis) wired to run the boiler on pump overrun but not the pump? or could it be a PCB fault?.
Possibly by wiring the pump directly from terminal 7 and not connected to PL on the boiler and terminal box?. and connecting terminal 10 (as well as terminal 7) to L on the boiler terminal box.?.

 

[SJB060685]

I assume you're referring to the image above John. The SL (switch live) you see will be demand from system and starts the boiler sequence. The pump live will most likely be switched from the permanent live into boiler block and continue energising pump for a set time after the burner has shut down.
Of course without seeing something in person we can only ever guess whats happening and where.
Personally I think the op should employ the help of another engineer and have it thoroughly checked over.

 

[nut&bolts]

From discussions, I undertand that I have a W style system where hot water is prioritised. Knowing from the discussions about how the triport valve works. . I did the following:
1. Used all hot water so that water in taps becomes cold
2. Heated the water for 30mis and sitched off
3. Turned central heating for 5 mins and switched off. I assumed that the valve position now would be in its last used place ie; CH and way towards hot water cyclinder would be closed.
4. This evening I checked the water temprature felt normaly hot in the taps and it has not been overheating.
5. I touched all the pipes in the airing cupboard and noted that pipe diverted to central heating was HOT (It shouldn't be as CH has been off since morning. Although no rads are hot). The hot water pipe that goes to the cylinder after the valve was cold. It appears that boiler has been still firing up now. The water has been going toward the pipe that feeds radiators. Pump has been alwatys off.

Does this rule out fault of valve? and supports what is being said that wiring/ electric connections are at fault?

 

[SJB060685]

W plans do not hold the last port off call like a Y plan does. It is a diverter valve which should spring return to HW port once CH demand has ended.