Central heating pump only comes on when hot water is on...

[danjf]

I've had loads of problems with my central heating system recently. First off the circulation pump jammed up with debris. Managed to clear that out and get the pump running nicely but now I have another problem...

The pump is only starting when I switch the hot water on as well, I also have to have the thermostat on the hot water tank turned up fairly high for this to happen (Get the pump going)... to about 70-75.

Any ideas, could it be another blockage somewhere?

Planning on doing a full flush and clean soon.

 

[Softus]

The pump is only starting when I switch the hot water on as well

How many motorised valves do you have?

What programmer?

Have you knowingly changed any wiring?

Any ideas, could it be another blockage somewhere?

Well, if the CH zone valve was sticking, it might not fully open and reach the point of closing the microswitch.

 

[danjf]

We have honeywell control system. The thermostat on the hot water tank is a honeywel L641A1005. When the hot water is switched on (through the H525 Horstman controller) it fires up and the heating circulation pump starts, for a while but then stops.

If I then turn the hot water tank thermostat up the pump starts going again.

Coming out of the hot water tank we have a junction box, which seperates the water into the hot water taps and central heating (Via the pump).

The biggest problem is that the central heating pump will not start running unless the heating is also on, and only then when the tank thermo is turned up fairly high.

Could it be my control setup is knackered?

Thanks in advance.

 

[petit_pablo]

Sounds like its either the motor in the powerhead or the ball in the actual diverter body.

If you push the little lever on the silver box across to the right as far as it will go, does the heating come on?

 

[danjf]

Yes, it did once or twice yesterday... but not now. Not today.

The pump now only comes on when:

1. The hot water is switched on (On the timer controller)
And
2. The tank thermo is turned up fairly high (I suppose this is the system asking for more hot water from the boiler?)

When the pump is running the radiators do heat up.

 

[Softus]

We have honeywell control system. The thermostat on the hot water tank is a honeywel L641A1005.

But how many motorised valves do you have?

When the hot water is switched on (through the H525 Horstman controller) it fires up and the heating circulation pump starts, for a while but then stops.

If I then turn the hot water tank thermostat up the pump starts going again.

That sounds like normal operation to me.

Coming out of the hot water tank we have a junction box, which seperates the water into the hot water taps and central heating (Via the pump).

You probably have at least four connections to/from the hot water cylinder (aka tank). Which of these connections are you referring to, i.e. where is it? For example, I'm expecting you to say that it's on the side, about halfway up the tank, with another connection near the bottom on the same side. Is it?

And when you say junction box, is that a motorized valve, with a black cable connected to it, and three 22mm (or 28mm) pipes? Does it have "Honeywell" marked on it?

The biggest problem is that the central heating pump will not start running unless the heating is also on, and only then when the tank thermo is turned up fairly high.

Could it be my control setup is knackered?

No. There is no such valid description for a set of central heating controls. They are a collection of discrete components that are designed to work in concert, any one (or occasionally, two) of which can fail at any given moment. Correcting the fault is a matter of determining which component is faulty, and either fixing it or replacing it.

There are no valid guesses, or suppositions, or assumptions that you can make. The method of fault-finding is to ask you what components you have and how they behave when you operate the user controls.

Do you have a room thermostat? If so, what model or type is it?

Also, if you have a digital camera then a photo of the cylinder and pump connections might prove useful later on.
__________________________

Sounds like its either the motor in the powerhead or the ball in the actual diverter body.

Oh it does, does it? So how have you determined that it isn't the room thermostat, or the programmer, or a loose connection, or a microswitch, all of which are possibilities?

If you push the little lever on the silver box across to the right as far as it will go, does the heating come on?

Why would the heating come on?

Pushing the lever will move the valve (if it's not broken), but unless you shove the lever hard and fast so that the momentum carries it beyond the position of manually driven travel (which, BTW, would risk breaking the mechanism), then how will it actuate the microswitch?

 

[danjf]

This shows the main pipework... the pump was badly glogged up but I removed and cleaned it up and is working well now (Please ignore the mess in there, this is work in progress!).

You can see the switch in the middle there, its a Honeywell v4073 type 3 port switch. Yesterday when I switched it to manual the pump started to circulate hot water to the radiators. Back on auto this has stopped and today when I switch it to manual it doesn't work anymore.

The pump works fine when the hot water is switched on (Expected) and the radiators do get hot in this situation... only until the hot water reaches the correct temperature and then the pump switched off (Expected).

I'm thinking the 3 port switch may be blocked in some way which then not letting the controller know when to activate the pump?

This shows the pipework into the pump.

Our controller is a H525 Horstman and we do have a thermostat in the hall (Honeywell).

Thanks again all!

 

[Agile]

Pipework done by apprentice or trainee!!!

Tony

 

[Softus]

This shows the main pipework.

Good work danj.

You can see the switch in the middle there, its a Honeywell v4073 type 3 port switch.

I wouldn't call it either a switch or junction box - it's a motorised valve.

Yesterday when I switched it to manual the pump started to circulate hot water to the radiators. Back on auto this has stopped and today when I switch it to manual it doesn't work anymore.

The concept of 'manual' doesn't apply to a 3-port valve, because it can never be closed. All you're doing it moving the valve to divert water to either CH, or DHW, or both.

The pump works fine when the hot water is switched on (Expected) and the radiators do get hot in this situation... only until the hot water reaches the correct temperature and then the pump switched off (Expected).

This would be expected only if the room thermostat was not calling for heat.

I'm thinking the 3 port switch may be blocked in some way which then not letting the controller know when to activate the pump?

That's not how the system works. The programmer provides an electrical supply to the room thermostat that, when its switch is closed, continues to the motorised valve.

If you can determine how far that electrical supply is getting, then you'll be close to diagnosing the problem. You need a multimeter, and the knowledge to work safely with electricity.

Room thermostats and motorised valves are common failure points. Programmers less common.

You could remove the powerhead from the valve, and see if the actuator moves at all when you operate both thermostats. If not, then it's likely to be the motor. You can replace the motor on its own, but most people replace the entire powerhead. Some people always replace the entire valve.

 

[Softus]

Pipework done by apprentice or trainee

Rubbish. Plenty of experienced people could be responsible for that pipework. Some of them are formerly radio engineers, wear checked shirts, and show off a lot.

 

[danjf]

I'll check the valve later today, and post back here.

I have just picked up a new one from ebay, as it was going cheap. Will replace it even if not the problem when I drain the system later this month as it does seem to have a lot of scale build-up.

 

[danjf]

Looks like it is the motorized valve. Opened it up and had someone turn on the heating and it was trying to turn the valve but was struggling. I've turned it a few times and loosened it up a bit and is now working - for the time being anyway.

New valve on its way which should (Figures crossed) solve the problem long-term!

Thanks again for the advice.