Vokera Maxin 28e - intermittent hot water

stressout · 9 Mar 2006

The background to this is that about a month ago we had rads off and new rads on so the system was drained twice. Since then our HW supply has been poor (takes ages to heat up, then cuts out) and it's getting worse. It took about half an hour to run a very shallow bath for my daughter last night. I'm wondering if anyone has any ideas what the problem could be and if it could be related to the system being drained. Number of rads on system is two fewer than before, but we have added a new kitchen area and there is new piping to there - not yet in full use but the kitchen fitter did some work on them yesterday.

Thanks in advance for any help.

Agile · 9 Mar 2006

We dont really have enough information to come to any opinion on whats wrong.

You probably have a gravity hot water system.

My best guess is that the heating system is stealing all the heat and preventing the HW from getting enough.

You could test this theory by closing the one adjustable valve on each rad and see if the water then heats up quicker.

Tony

kevplumb · 9 Mar 2006

it's a combi tony

ChrisR · 9 Mar 2006

I don't understand Tony's answer. This is a combi...

HW not working is usually a problem with the diverter valve or its diaphragm. Turn a hw tap on full and feel the CH pipes under the boiler. If leftmost fat one is getting hot then diagnosis confirmed.

Not connected with draining the system.

stressout · 9 Mar 2006

Plumber has been - it's either a sensor (can't remember exact name) or the PCB! Does that make sense given the problem that I posted? He says it's def not related to the other work they did for us last month, but my husband is not convinced it's a coincidence! I tend to believe the plumber as he is a straight guy and knows his stuff. Am I gullible? He's gone for the sensor first (as cheaper) but is ordering PCB as fallback.

ChrisR · 9 Mar 2006

From what you say I'd check for the diaphragm first, once I'd saved up the £3.50 to buy it

. Maybe he's been in there and found out more. But pcb sounds unlikely

.
Go grope that pipe as I indicated - it'll take you several seconds...
HW and CH water are not connected, unless what was done has put rusty boiler sludge into the boiler, which seems a) unlikely b) not the plumber's fault!

stressout · 9 Mar 2006

Thanks ChrisR for the swift response. From where I was sitting (working away on my laptop) I could see him testing things and he was running the hot water while doing it. He says it's def not the diaphragm (sp?). I told him i'd been investigating online. He's ordering the control board just in case, but he said he had fiddled with some elements in it and they seemed to respond so that's what made him think it might be more than the sensor, but as the sensor is cheaper he's going to try that first. How much would these parts cost as a rough estimate?

++++++++++++++++++++++++++++++++++++++

Meant to add - I tried your tip, ChrisR and there are sooo many pipes feeding into and out of my boiler that I'm not sure which one to use. In any case, the hot ones that I could find were more 'warm' than hot - I could very comfortably wrap my hand round them. Water coming out of tap was ice cold.

MOD 2

please use the edit button

stressout · 9 Mar 2006

We've got almost no hot water now. Get a short burst when initially turn a hot tap on, but then nothing. CH still OK.

The plumber is certain it is either a sensor OR the PCB so both have been ordered with installation hopefully tomorrow pm. Does that sound right? To be honest, we had a similar problem with a shower pump a few years ago - where the problem started and then got worse and worse and it was the PCB in the end so maybe he's right. I'm just worried that he'll replace those tomorrow and we'll still have no hot water.

weargas · 9 Mar 2006

I'd say your dhw heat exchanger is scaled as a result of the constant ingress of fresh water via 2 draindowns/re-fills without inhibitor, find out if inhibitor was put in on the refills. If its the sensor or the pcb it's the first i've heard of on a maxin. Are you in a medium/hard water area?
Get the plumber to run the hot tap and feel the dhw heat exchanger. If it burns his fingers (sometimes only on one side, depending how badly scaled it is) and the water leaving the boiler is barely warm then the money is on a dhw heat ex.
Tell him if the pcb doesn't cure the problem then you aren't paying for something you didn't need as it's down to his false diagnosis.

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Vokera Maxin 28e - intermittent hot water

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