Boiler pump runs continuously - what is wrong?

justinhow · 21 Mar 2011

I have a Bosch Worceter Greenstart 24i system boiler.
My system has 2 zones and 2 motorised valves.
It uses a Heatmiser 2 channel Wireless Programmable Thermostat.
The problem is that the boiler pump seems to run continuously in the boiler (24 hours a day). Recently it burnt out and was replaced under warranty.
This problem appeared to exist (at leat intermittently) on the system before the old boiler was replaced (the valves were not replaced). All appeared to work ok for the 1st month or so of use after the boiler was put in.
I want to avoid this happening again and could do with advice as the the likely location of the fault so I know who should be looking at it.
1. Boiler (over run not working properly?)
2. Motorised Valve
3. Heatmiser Porgrammable Thermostat.
4. A wiring fault.
or..
The plumbers have asked Bosch Worcester to look at the boiler and a BW engineer is coming out tomorrow but I expect will say their boiler is working fine.
Any help would be greatfully received.

D_Hailsham · 21 Mar 2011

justinhow said:
I have a Bosch Worceter Greenstart 24i system boiler.

The problem is that the boiler pump seems to run continuously in the boiler (24 hours a day). Recently it burnt out and was replaced under warranty.

The plumbers have asked Bosch Worcester to look at the boiler and a BW engineer is coming out tomorrow but I expect will say their boiler is working fine.

The pump on a Greenstar 24i System boiler is inside the boiler and controlled by the boiler. So the fault is more than likely to be boiler related.

justinhow · 30 Mar 2011

Ok - The Bosch Worester Engineer came out and said it was not a boiler fault.

He said that there was 240v permamntly on the Live Return to the boiler and this would make the boiler pump run all the time. He said this should be switched by the programmer/valves.

He thinks it probably is a wiring fault. Where would the live return normally be connected to at the other end?

I want to make sure it is not a fault with the Programmer (Heatmiser) as the plumbers did not purchase/provide this themselves, although they did wire it up, and they will disown any problem with it.

Agile · 30 Mar 2011

I dont know what he means! At least not based on what you are saying!

He probably means there is a call for heat but that would make the boiler heat itself up if the zone valves were both closed. That could be caused by a stuck microswitch in a motor valve!

Does it fire up and keep itself hot ???

The next question is do you have an auto bypass valve?

It seems odd the fault was apparently not noticed when the pump was replaced! Was it a nupty engineer just interested in getting out of the house without bothering to check everything?

Tony

justinhow · 30 Mar 2011

I personally think it might be a valve problem because the exact same problem occurred on the old boiler since when:

The Boiler has been replaced
It has been re-wired
The Programmer has been replaced

How could I check this myself?
The heating is definitely not on all the time - I will check about the hot water though.
And yes the previous engineer did pretty much no tests at all. To be fair to him only my wife was in and he did not know how to operate the programmer.

justinhow · 30 Mar 2011

In the pic shown it is the terminal block at the bottom that is the one in the boiler and I think it is the switched live (far left terminal) that is powered all the time currently which the engineer said should not be (I guess that must be correct as it says switches live!)
The manual that has this pic in says: "Connect SWITCHED LIVE wire from terminal (Lr) to the boiler demand on the system wiring centre." So where would this normally connect to?

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justinhow
30 Mar 2011
1

Agile · 30 Mar 2011

justinhow said:
The heating is definitely not on all the time - I will check about the hot water though.

I dont mean the heating, I only mean the boiler!

It would run to keep just itself and the pipes to any bypass hot. It would refire for a couple of minutes every 20-30 minutes.

THATS the key to identifying the fault.

Tony

petit_pablo · 30 Mar 2011

Switched live comes from motorised valves.

Take a look in main wiring centre, there will normally be an orange wire from each of these valves.

Make sure you turn the power off before you go poking about in there mind!

Do you have access to a multimeter?

justinhow · 30 Mar 2011

Guys thanks for your excellent posts - they coincided with me finding diagram from installation manual of Programmer/timer which confirms that the Switche Live is controlle by Micro Switch in Valve which I think has probably gone faulty.

This looks more and more like a motorised valve issue to me.

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justinhow
30 Mar 2011
1

justinhow · 30 Mar 2011

and yes I do have a multimeter

petit_pablo · 30 Mar 2011

Mulimeter, Lovely!

You can check the valve switches to find which one is stuck.

Method 1. Turn off power, set meter to ohms.

Pick a valve to test and disconnect the perm. live (usually grey) and the sw.live(orange). Make a note of where you removed them from!

Check with the meter between the 2 disconnected wires. Open circuit suggests that switch is ok, continuity suggests the switch is stuck.

Do that on both valves.

Method 2. Power off.

Disconnect one of the orange wires and make it safe with a terminal block on the end. Turn power on but timer off

Use Vac on the meter and test the removed orange wire and the orange wire you have left in the wiring centre. One of them will have power on it. Thats the faulty one.

justinhow · 30 Mar 2011

petit_pablo - Superb - will go with method 2 I think. Will post results. Wife will post results of all goes horribly wrong

Great forum and most helpful.
Justin

petit_pablo · 30 Mar 2011

Method 2 is quicker. Just be careful with 240v

justinhow · 31 Mar 2011

Well I tested as per method 2 and confirmed that the hot water Sunvic valve was faulty providing 240v permanently on the SL.

I have ordered a Sunvic SZ2301 actuator replacement for it and hopefully all will be ok in a few days.

Again thanks for the help.

Ctmt · 31 Aug 2012

I am having the same problem following a new boiler installation. Did you ever resolve this? I am using the f100 controle unit with solar panels also attached.

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Boiler pump runs continuously - what is wrong?

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