Worcester 28CDI hot water problems

[Maxsys]

Hello all,

Little help if you wouldn't mind, i have an issue with the hot water on my Worcester 28CDI, been in for about 6 years, about two years ago i replaced the diverter valve as i could only get hot water whilst the heating was, on, pig of a job but did the trick. Now i have a different issue, i can get hot water without the heating being on, but only if i turn the tap flow rate down, and even when i do this the boiler cuts out now and then and then refires. It takes ages to fill a bath, and is causing problems with my showers. After doing some digging around on here and on tinterweb i suspect the water to water heat exchanger is scaled, am i on the right track?

If the hot tap is on full i only get luke warm water, its almost as if the boiler cannot heat it up quickly enough. It was not like this when first installed, but i suspect has deteriorated over the years without us really noticing, we started turning the tap flow down on the bath about a year or so ago, but not as much as now.

should i be measuring the flow rate from my taps?, could it be a gas problem, in which case i will have to get a man in, should i be checking the pressure in the expansion vessel, or have i missed anything?

Pressure guage is always constant no loss

I am thinking at the moment replace water to water plate exchanger, and while i have it in bits replace the diaphragm in the diverter valve, just while it is in bits as i know they are prone to problems.

Thanks in advance.

 

[Maxsys]

Anybody?

 

[cross thread]

could be various reasons ,gas pressures ,thermistor ,scale,air pressure save money and get a eng to look instead of wasting money on parts that mighn not be needed.worcester do a fixed price repair i think

 

[Agile]

As stated it can be caused by several different problems or even a combination of them.

To try to see how the plate HE is operating you need a contact thermometer to measure the flow/return temps.

To check the power input you could measure the power consumed at the gas meter, see FAQ. BUT that will have been reduced if the plate HE is blocked.

There is a lot more to correctly diagnosing faults on boiler than may meet the eye.

I always recommend calling a good boiler engineer!

Tony

 

[Maxsys]

Thanks for the responses, i have a non contact infrared thermometer so i can measure the temperatures at the flow and return, i assume they should be the same?

I think Worcester fixed price repair is about £200.

To be honest for the sake of £80.00 i think i will change the plate exchanger, DHW thermistor and the diverter valve diaphragm, if it still does not solve the problem i get an RGI to have a look, fortunately my son has just started a Plumbing apprenticeship, so i have a man i can go to, if i can't fix it myself.

Thanks again for the responses.

 

[Agile]

Thanks for the responses, i have a non contact infrared thermometer so i can measure the temperatures at the flow and return, i assume they should be the same?


if it still does not solve the problem i get an RGI to have a look, fortunately my son has just started a Plumbing apprenticeship, so i have a man i can go to, if i can't fix it myself.

Thanks again for the responses.

I said that you need a CONTACT thermometer! An IR thermometer is virtually useless for that ! ( emissivity and shape factor )

The temp diff should be a max of about 15 C. If much blocked it can reach 25-35 or higher.

Someone starting a plumbing apprenticeship will not be qualified to work with gas and will not normally have much experience of boilers for at least three years with most firms. Will be installing bathrooms and radiators! Not fixing boilers!

Tony



PS Nice to hear someone is doing a proper apprenticeship rather than a short course!

 

[Maxsys]

Thanks Tony,

OK i get the thermometer thing, i might have a contact one in my shed.

As for the apprentice i did not mean my son looking at the boiler, i meant the guy he works for, my son would open the cupboard and go "yes dad that's a boiler" now speak to my boss LOL.

Your right, rads, bathrooms and general dogs body at the moment, but he loves it, it's a three year course with a local company and local college, one day a week for 8-9 hours a day, bit different from school but he is only sixteen and keen to learn, and at least he is willing, unlike many 16 year olds. Gas comes in the fourth year and he says he wants to do it, so lets see what happens.

My older son is 17 and in his second year of a 3 year carpentry apprenticeship, just need to get my 14 year old daughter interested in electrics, and jobs a gud 'un, can't see it happening though.

 

[Maxsys]

Quick update,

Replaced the DHW sensor tonight as it is the cheapest bit, no luck still the same issue,. so i have ordered a new plate exchanger and diverter valve diaphragm, might as well do that while i have access.

Will post back in a couple of days with a result, hopefully the right one!!!

 

[Maxsys]

Got a multimeter with temp probe, here is a pic showing the readings with the bath hot tap on, and in all cases the temp when the boiler cuts out and then fires again, noticed the CH flow and return getting hot as well so maybe the diverter valve is letting by, opinions please

Untitled

• Maxsys
• 15 Nov 2011
• 1

 

[Gasman81]

PS Nice to hear someone is doing a proper apprenticeship rather than a short course!

Didn't you do a short course Tony?

 

[Maxsys]

So anybody got an opinion on the temps?

 

[Maxsys]

Now sorted, changed the plate exchanger and shower is now hot, and boiler does not switch on and off