This looks like a c plan gravity system to me. If it is it needs a descale.
Problem with insufficient hot water
- Thread starter spiceyokooko
- Start date
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What's a c plan gravity system and how would I descale it?
Thanks.
Thanks.
Download Honeywell wiring plans from their site and you will find a C Plan control layout. It was an upgrade from a gravity system to allow temperature control of the hot water. Gravity primaries had a habit of scaling up preventing good gravity circulation. I haven't seen a gravity system for many years. I descaled one about ten years ago. Can't remember how. Used a power flushing plant with Kamco fx2 descale chemical. This is a job for an expert.
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Thanks for your input comment.
Whilst I do live in a hard water area and scale can be a problem here (and I have no doubt the system would benefit from a descale) I just can't see how that could be causing the problem I'm experiencing.
The pressure from the hot water taps is fine, it's the temperature of the water that's the problem - there's just not enough hot water coming out. In other words the system simply isn't heating up enough hot water.
The hot water cylinder has an electric immersion heater element in it, but I've never switched that on ever since I've been here, which is about 20 odd years now. I don't even know if it works.
Here's a diagram of my hot water cylinder - the one on the right, the indirect system. It's precisely the same as the one I have, except mine has a thermostats on it.
http://www.diydoctor.org.uk/projects/domestic_hot_water_systems.htm
Are you saying the heat exchanger in the hot water cylinder is so scaled up it's not able to heat the water correctly?
Well that's my hunch.
I think I'm going to change the motor in the two port valve and the thermostat on the hot water cylinder and see if that fixes the problem.
If it doesn't, I suppose I'll have to call out a plumber.
Before you replace the motor and stat. Lock the valve open with the lever at the end of the valve. Run your heating for the next hour with the room stat turned up high. If you have no hot water after an hour think again. If you do it's controls.
To answer you earlier comment. The scale I was talking about forms in the primary pipework and is not caused by hard water. It has no effect on hot water flow only the temperature.
You said you are getting warm water. This implies you have partial circulation. If you do then the zone valve must be letting by. Either because it is faulty or open. Do you own and can you use a multi meter? If so you can track the fault without replacing any parts UN necessarily.
Have you determined what system you have? ie C plan
If you are getting warm water and the valve was not opening it must have been letting by. If this is the case it should be replaced body as well.
To answer you earlier comment. The scale I was talking about forms in the primary pipework and is not caused by hard water. It has no effect on hot water flow only the temperature.
You said you are getting warm water. This implies you have partial circulation. If you do then the zone valve must be letting by. Either because it is faulty or open. Do you own and can you use a multi meter? If so you can track the fault without replacing any parts UN necessarily.
Have you determined what system you have? ie C plan
If you are getting warm water and the valve was not opening it must have been letting by. If this is the case it should be replaced body as well.
Thanks for your reply.
I've looked at the wiring diagram and as far as I can tell it is a c plan. There is a wire from the cylinder thermostat to the control valve, and one to the timer switch. So presumably when the timer is set to hot water on, the thermostat is telling the control valve whether to fire the boiler based on the cylinder temperature? The thermostat for the CH is downstairs and again from memory is set quite low, would that be having an affect on the water temperature?
I'll check the control valve setting but from memory I think it's set to open all the time anyway, which is the only way I could get hot water from the system. I'll check on that though with what you suggest.
Yes, I have a multi-meter that can do voltage measurements etc.
I'll get back to you once I've done some checks.
Thanks.
I've looked at the wiring diagram and as far as I can tell it is a c plan. There is a wire from the cylinder thermostat to the control valve, and one to the timer switch. So presumably when the timer is set to hot water on, the thermostat is telling the control valve whether to fire the boiler based on the cylinder temperature? The thermostat for the CH is downstairs and again from memory is set quite low, would that be having an affect on the water temperature?
I'll check the control valve setting but from memory I think it's set to open all the time anyway, which is the only way I could get hot water from the system. I'll check on that though with what you suggest.
Yes, I have a multi-meter that can do voltage measurements etc.
I'll get back to you once I've done some checks.
Thanks.
The room stat should not effect the water temperature. The boiler stat may. Try turning up the boiler stat and lock the valve open. Turn up the room stat to ensure the boiler is kept on if water controls are faulty. If you don't get hot water it is almost certainly scaled up. I interestingly had a similar situation yesterday. A system that had been upgraded from gravity to fully pumped had stopped working on hot water. I flushed out the primaries with Mains water and removed a plug of debris. It's now working. Next I will fire the boiler in hot water only. Measure the gas consumption and the temperature change across the flow and return. From this I can calculate the heat transfer to the cylinder. If it is to low I will recommend a descale or a new cylinder with a higher rated coil.
You confirmed that you have a multi meter. Are you able to follow the logic of the c plan wiring diagram. If so you can test it. If not I can try to guide you. May be easier by phone. I'm not sure if offering telephone advice contradicts any protocol for this site but I'm sure the other engineers will let us know.
You confirmed that you have a multi meter. Are you able to follow the logic of the c plan wiring diagram. If so you can test it. If not I can try to guide you. May be easier by phone. I'm not sure if offering telephone advice contradicts any protocol for this site but I'm sure the other engineers will let us know.
Hi easyas, thanks for your comments.
Okay I did some tests on the system.
I switched the 2 port valve to the open position and let the central heating and hot water run this evening for 3 hours or more and was able to get a decent supply of hot water from the system.
Why does the central heating need to run to get any hot water from the system?
Does that suggest that the 2 port valve motor and/or micro-switch isn't working?
I can follow the wiring diagram if you can let me have instructions on how to test.
Many thanks!
Okay I did some tests on the system.
I switched the 2 port valve to the open position and let the central heating and hot water run this evening for 3 hours or more and was able to get a decent supply of hot water from the system.
Why does the central heating need to run to get any hot water from the system?
Does that suggest that the 2 port valve motor and/or micro-switch isn't working?
I can follow the wiring diagram if you can let me have instructions on how to test.
Many thanks!
Turning on the central heating was just to ensure the boiler was running. If the valve is open and the boiler running then if there is no scale the primaries will flow due to differential buoyancy. You have now proved you have a controls issue. The sequence for the controls can be checked with your multi meter. Starting at the programmer. Do you get a live feed out for hot water? If so is there a signal to the brown wire at the syncron motor in the zone valve?
No signal from the programmer = faulty programmer
No signal to syncron motor = faulty cylinder stat.
Signal to syncron = faulty syncron.
this assumes all controls are set to call and that the valve isn't opening when controls are calling.
If you have a signal too the syncron and it doesn't open replace the entire valve.
No signal from the programmer = faulty programmer
No signal to syncron motor = faulty cylinder stat.
Signal to syncron = faulty syncron.
this assumes all controls are set to call and that the valve isn't opening when controls are calling.
If you have a signal too the syncron and it doesn't open replace the entire valve.
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