Vaillant EcoTec system boiler doesn't heat water in summer

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I'm not a central heating engineer, but neither my central heating installer nor Vaillant have been able to solve my problem.
I had a Vaillant ECOtec plus 428 open vent condensing boiler fitted in November 07, replacing an ancient Servowarm system. Lots of new valves, pump, room thermostat, timer needed, but old radiators and immersion heater.

Over the winter I noticed the boiler kept switching on for a couple of minutes, then off for a few minutes, then back on again.... and my house was no warmer than with the Servowarm. I got adequate hot water. I wasn't impressed by the amount of gas I used - very similar to the Servowarm.

Now it's summer the central heating is off, and the hot water is not as warm as it was in winter - in fact inadequate for a hot bath, and it seems to take longer to heat up. To get a hot bath I have to switch on the central heating (2 radiators on) for an hour at the same time as the water heating is on.

I have observed the boiler closely. This is with the central heating off. I switch the hot water timer on. The boiler fires up, and runs for a few minutes. The temperature indicated on the boiler display zooms up to 70C, then the boiler flame display goes out. The temperature indication drops pretty quickly. The pump is still running. After about 3 or 4 minutes the boiler reignites, but only runs for less than a minute before being off for another 3-4 minutes, by which time the temperature indicator is down to 40C ish.
If I put the central heating on too, a similar thing happens but the period of boiler running is longer.

My amateur diagnosis is that the anticycling feature is kicking in and the overall effect is that there is only hot water in the heating coil in the hot water tank for about 30 seconds out of every five minutes. Hence the tepid water and taking ages to warm it much at all.

Any advice? What can I do to get proper hot water?
 
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It sounds firstly as though there is no circulation in your system.

Check the pump is working.

You also need to ascertain whether the system has been wired up correctly. Your pump should be wired back to the appropriate terminals on the boiler.

Other than this it could be a 3 port valve, or 2 port valve fault.

Check the above then post back.
 
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I can feel the pump vibrating gently when it is on, and not when it isn't. When I switch the central heating on, hot water gets into the radiators. The central heating engineer has checked the valves. I can feel the pipes at various points, and when I start the boiler from cold (not been on for an hour or so) I can feel the progress of hot water around the pipes to the hot water tank and back again.
 
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I am concerned that a 7 month old system is not getting sufficient support from your Fitter or Vaillant (especially as I am about to have a Vaillant EcoTEC 630 fitted). What have support have you had? Is your fitter recognised by Vaillant?
 
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Next is to check for air locks and possibly muck in the HE. Was the system powerflushed properly when the boiler was installed?

Has the boiler been commissioned properly with an FGA by your installer? They are not a fit on the wall and it will be ok type of boiler.

Read your service manual and set the boiler to d40 and d41 alternately whilst it is firing.

What does what do they both read?

Has your engineer checked that the thermistors in the boiler are still attached correctly?
 
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OK. The boiler has been off for about 4 hours, but the hot tank is still warm (not hot - does need more heat). Then I flick the timeswitch, and leave it switched on for the remainder of the test.
D40=26, D41=25
Pump on
D41 drops to 16, didn't catch D40
Boiler on
D41 rises to about 46 by the time the boiler switches off again (about 1 min) D40 rises to 72
The boiler starts off quite quietly, then makes a roaring noise, as if it is working quite hard. But only for a few seconds. Once D72 has risen to 72 the boiler goes off (pump still on).
Boiler off
D40 rapidly drops to around 45, and D41 to 48.
D67 is 3
State is S.7
After 3 or 4 min D40 is 46, D41 is 47, pump is still on.
The boiler comes on again
D40 rises rapidly to 72, D41 is at 44
The boiler switches off again, after only about 10 seconds of on time and goes to state S.7 again.

When the Vaillant engineer checked the boiler (which was back in March when I hadn't discovered the summer hot water problem, but was worried about inefficiency and the fact that the boiler kept switching on for a couple of minutes, then off for a few minutes, then back on again) he found no problems. He was concentrating on the efficiency aspect and had didn't take the on/off aspect seriously - at that time, with the central heating on, the boiler would go on for about 4 min and off for maybe 2 min.

It seems to me the boiler is being overenthusiastic about heating the water, gets it too hot, then switches off for the anti-cycling time. Is this supposed to happen, or is the boiler supposed to moderate its heat output to match what is required for a steady flow of the right temperature water round the system? Is a modern boiler really supposed to operate in this start/stop mode?
 
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The d40/d41 figures are a bit inconclusive, but the general trend to me is that the differential is too great, indicating possible partial blockage in the HE or possibly the pump.
 
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I would be looking at the old pipework going to the cylinder, cold feed into system and for any balacing valves / bypass valves that may be inappropriatly adjusted before I went down the faulty boiler route.
 
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The d40/d41 figures are a bit inconclusive, but the general trend to me is that the differential is too great, indicating possible partial blockage in the HE or possibly the pump
The differential is only great for a few seconds whilst the boiler is apparently running flat out (it sounds as if it is, anyway).
 
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I think the problem is actually what you suggested but you were unable to realise just why thats happening.

You have a 28 kW boiler running flat out.

Quite simply, unless you have a 10 bedroom house your boiler is massively oversized for the house!

Look in the manual and see if it has instructions for reducing the maximum power output. This should be included in the service manual but might not be.

Reduce it to minimum ( about 9 kW ) and tell us the result.

Whats the style of house and number of bedrooms? What colour is the hot water cylinder?

Tony
 
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Hi All

Spot on Tony. During ignition phase and the first minute of operation the ecotec 400 series ramp up very quickly to full output before dropping down to the range rated input. If there is a lockshield valve on the cylinder return partially closed, the pump is on 1 or 2, or crud in the heat exchanger coils, then 28kw (factory setting) into that situation soon turns the boiler off.

Bullet points for good commissioning for these appliances are:

1. Fit a good pump (6M head better than 5M but system dependent) set to highest speed. Check isolation valves are fully open. Wire to the pump terminals on the boiler pcb! Also check pump impeller for blockages!!

2. NO restriction on cylinder return. Valve if you must for flushing or isolation, but leave open full bore. Avoid Ball-o-fix type valves.

3. Set heating load correctly to system. Remember in the real world with TRVs etc your full heating load will probably be used less than 10 days of the year. A good rule of thumb is 1.4kw per rad. This should average out for postage stamp rads/ big doubles. Personally I don't allow any additional requirement for the Hot Water, leaving the cylinder stat to control that side of things.

4. Fit an ADVO or similar auto-bypass set to 2.5M head (not a ball-o-fix cracked open!). Make sure its fitted after the pump and before any zone valves.

5. Flush, flush, flush...!

6. Always fit an interlock for heating i.e. a room thermostat.

If after this you still have problems the pipework is wrong or theres still old system sludge in the heat exchanger coil.

Hope that helps

The Bunny
 
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Great - an explanation that fits the facts! Thanks for listening and replying. Turning down the heating load control on the boiler improves the situation, but doesn't completely solve it.....
Whats the style of house and number of bedrooms? What colour is the hot water cylinder?
Ground floor flat (5 main rooms) of large and draughty Victorian stone built house with masses of large single glazed windows. 8 radiators, of which 7 have thermostatic valves. The hot water cylinder - well, it's covered in yellow insulation - it is not new, not Vaillant.

Bullet points for good commissioning for these appliances are:

1. Fit a good pump (6M head better than 5M but system dependent) set to highest speed. Check isolation valves are fully open. Wire to the pump terminals on the boiler pcb! Also check pump impeller for blockages!!

2. NO restriction on cylinder return. Valve if you must for flushing or isolation, but leave open full bore. Avoid Ball-o-fix type valves.

3. Set heating load correctly to system. Remember in the real world with TRVs etc your full heating load will probably be used less than 10 days of the year. A good rule of thumb is 1.4kw per rad. This should average out for postage stamp rads/ big doubles. Personally I don't allow any additional requirement for the Hot Water, leaving the cylinder stat to control that side of things.

4. Fit an ADVO or similar auto-bypass set to 2.5M head (not a ball-o-fix cracked open!). Make sure its fitted after the pump and before any zone valves.

5. Flush, flush, flush...!

6. Always fit an interlock for heating i.e. a room thermostat.

1. Pump is at highest speed (3). Central heating engineer checked the valves 4 days ago.
2. I know of no restriction on the cylinder return.
3. I have today set the maximum power output to 7kW (but realise I may need to increase this in the winter when I want central heating)
4. At the moment the bypass is a manually adjusted valve, adjusted recently by the central heating engineer who plans to return and put an automatic one in. During my experiments I have closed this bypass temporarily.
5. I believe this was done when the boiler was installed 6 months ago
6. There is a room thermostat in the hall.

So, the results of reducing the max power output to 7kW are good but not perfect.
If the hot tank is full of cold water, and the boiler has been off for an hour or so, it can heat the tank adequately for a bath. It runs steadily for about 35 min and then goes into cycling on 20 sec and off 4 min (despite the fact that demand from the hot tank never disappeared, i.e. the thermostat on the hot tank didn't trip).

I still have the problem of the boiler immediately going in to a cycling on and off state if I momentarily switch off the hot water whilst it is being heated, then switch it back on again. Or more importantly if I want to top up the temperature of the water in the tank which has been cooling for say half a day. What happens is

I switch on hot water timer
Boiler leaps into life - lots of water vapour out of the flue
Flow temperature zooms from 54C to 72C in about 20 seconds.
The boiler then switches off and goes into anti cycling mode.
The return temperature stays at around 54C for about 45 seconds after the boiler first switched on (so I interpret that it takes 45 seconds for the water to get round the hot water cylinder circuit)
Boiler stays off for 4 minutes
Boiler leaps into life again, for another 20 seconds and the whole cycle repeats.
Can't see this can be putting much heat into my not-hot-enough water.

So for the first minute after firing, does the Ecotec boiler ignore the fact I've restricted it to 7kW? That's the impression I get from its behaviour.

Is there anything I can do about this? I can't be the only person with a large boiler, who just wants to re-heat some warm water with no central heating.
 
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Basically you are suffering from the effect of having an over sized boiler!

On your HW, the heat absorption of the old cylinder is too low once the water around the heating coil inside has started to warm up.

A slight improvement could be obtained by increasing the temperature of the boiler output.

Alternatively reduce the cylinder stat temperature!

The position of the cylinder stat comes into this equation too!

Tony
 
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