Worcester highflow 3.5 - Help with DHW & DCH - LONG !

[roadhouse1387]

Hi All.

I have a Worcester Highflow 3.5 Gas boiler which seems to have developed a fault and I thought I would ask you guys for some advice.
I will not be attempting any major repairs myself (simple stuff I can do i.e. resetting things, testing and so on), I will leave that to the experts. But I would like to hear you opinions even if its just so i can prepare myself for the shock of the likley final bill.

The problem is this....We normally leave the hot water on all the time and the heating on the timer twice a day.

Now when i turn on the hot water, the radiators get very hot very quickly, whilst the hot water does not heat up beyond tepid or hand warm, then goes cold. Meanwhile, the rads get hotter and hotter.

Also, because my gas meter is in view of the bioler, I can see that the meter is whirring away at full belt, as if a hot water tap or the shower was on.

All of this is happening whilst the heating is in the OFF position...!

So with the water on and the heating off, I can heat the house till the rads are bouncing but with no hot water.

Next, i tried turning the water OFF and the heating ON....

In this case, the rads again get hot and i notice that the hot water light is showing that the DHW is ON as well as the CH even though the DHW switch is showing OFF !. I also notice that the gas is being used at a much reduced rate.

Again, I can get a sinkfull of hot water and thats all but the heating is working overtime. At least now though, the boiler switches the heating on and off according to the setting of the CH temp setting dial (as long as i set the HW dial to off) thus regulating the temp.

I can get the temp and the preassure to stabalise at around 2.5 bar by setting the DHW to off and the CH to just below position one on the dial. At this setting the rads are hot (hotter than they should be at this temp) and the preassure shows around 2.5 bar....if i turn either of the dials higher then the temp goes through the roof along with the preassure.

I wondered if I have a broken/stuck 3 way valve ? and is there a way to free it or a reset procedure I can try ?

Many Thanks
Shaun

 

[chrishutt]

I wondered if I have a broken/stuck 3 way valve ?

Could well be. You will need to carry out some electrical tests to determine if this is the case. It may be just a failed motor (synchron type) in the motorised valve - these cost about £10 and are quite simple to replace if you are competent with electrics.

 

[roadhouse1387]

Thanks Chris,

I have a good understanding of elecronics so I feel I could do that repair no problem.

What testing procedure do you recommend ?

Cheers
Shaun

 

[chrishutt]

You need to know what the circuit diagram is for the control system and the motorised valve in particular. I think it may be the same as a Honeywell Y Plan or W Plan which you can find links to on this forum, but check the High-flow manual too.

If it's a mid position valve it will have a slightly odd wiring arrangement and micro switch arrangement. First I would check that the inputs to the valve are as they should be for each setting of programmer, etc. If this is so, open the motorised valve head and check the synchron motor. If this is Ok check any micro switches (and diode?).

Although an electrical fault is most likely, it is possible that there is a mechanical fault with the valve body, but you should be able to operate it manually via a little arm to confirm that it's not jammed.

 

[roadhouse1387]

Ok Chris,

Thanks for that, I will dig out the diagram and start looking.

I will let you know.

Many Thanks
Shaun

 

[chrishutt]

I've done a little research into this myself. The motorised valve is a diverter valve without micro switches (as in Honeywell W plan). It's simply a matter of determining if the synchron motor is driving the valve when the brown wire is live. This live is fed from a relay in the boiler. I've got a very large (20 Meg) pdf on the Highflow which I can email if you can't find anything. But there may be a circuit diagram on the boiler casing somewhere.

 

[COG]

Remove the tin cover on the diverter valve with the power off and atach meter to the two leads feeding the syncron motor with the power on and a dhw demand it should power up if so and it fails to move then it will require replaceing.

 

[roadhouse1387]

Thanks for all the advice.

I took the cover off the valve motor and checked that I could move the actuator ok by hand...no problem.

I then turned the heating on and saw that the motor turned the valve..the boiler now seems to working ok..!

I left it running for a few hours and saw the gas cut in and out as it should.

The only problem I have now is that one radiator is cold (i can get it to heat up by shutting off a couple of others) and I have noticed that the preassure is running at about 2.6-2.7 Bar... it would normally run at about 2 Max. At cold the preassure shows 1 Bar.

Is this something to worry about ? Its very close to 3 !

Thanks again for all the help

Cheers
Shaun

 

[chrishutt]

You have an expansion vessel problem. Lots of threads on this, plus something in the FAQ topic.

 

[roadhouse1387]

Thanks for that Chris, I will check up on the other threads.

The mad thing is that now the boiler is working perfectly !

The preassure has returned to 2 Bar and everything seems back to normal.

I have no idea what is happening .....

Many thanks for the help, i will check the other threads up and se where to go from here.

Thanks
Shaun

 

[roadhouse1387]

Turned the heating up a little and the preassure went up to 2.9,

I wonder if repreassurising the expansion vessel is all thats needed here ?

Chris, Would you mind sending me the PDF you mentioned at the start of this thread please ?

I have read the FAQ and providing the precedure given in the PDF is fairly straight forward I may do it myself.


Cheers
Shaun

 

[Bizint]

Hello! I have exactly the same problem that has been intermittent for a couple of years. I've come close to replacing the whole boiler, I'm finding it very frustrating. Did you hunt down what the actual problem and fix was in the end?

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10 year old post - pleast post a new one with just your symptoms.
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