Worcester 37CDI Combi - intermittent water fault.

[Aragorn84]

We've just moved into a new place, and within hours have had issues with the heating.

The system seemed to be working initially, producing heat and hot water as you might expect.

At some point in the afternoon the wife wanted to fill the fishtank, which requires warm water. Ran the tap at the kitchen sink, and it went warm for 5 seconds then stone cold. Turned tap off, waited, tried again, still stone cold, so she asked me for a look.

I had a look at the boiler, which had "u9" on the display, which reading online means its reached a primary temperature of 109c. The temperature was just sitting there, at 109c. With the tap running or not running, nothing changed.

So i pressed the power button on the boiler to turn it off, and then turned it back on. It whirred into life for maybe 2 or 3 seconds, the temp dropped down into the 90's and it stopped again. Power cycled it again and it dropped a bit further, but this time the boiler then started up properly and seemed to run the heating normally again, with the temp settling in the 60's.

Tried the tap again at this point, and the temp very quickly shot back up to 109c and it shut down again.

So i turned it all off and left it, cold nights sleep, brrr!

Next morning we called the solicitor to report the issue. The previous owner suggested trying to power the boiler off at the mains for a while and see if that helped it, and arranged a plumber to attend this morning.

Tried that. Once back on, the heating worked fine, but the hot water was still intermittent. We tried it a few times thru the day, sometimes it worked fine, other times it repeated its warm for a few seconds, then cold and "u9" on the display.

This morning, it has worked perfectly. We've both had a shower without issue. Guy came out and had a look. Said the pressure was a little high so he fixed that but otherwise didnt really find anything wrong. He said the DHW thermostat was "a bit high" and that he turned it down, but i'd already looked at that myself and it was at "e" (which appears to be around 2/3-3/4 on the dial) and not max.

I guess my main concern is this issue is the start of some component failing, and i'm going to get lumped with a bill very soon when it finally gives up. So i'm wondering if these symptoms are indicative of a particular fault. The fact the temperature seemed to get "stuck" at 109c seems somewhat odd to me. Especially when your drawing off water.

Any thoughts would be much appreciated.

 

[ianmcd]

The pressure being high and the selection of the temp control knob would have no bearing whatsoever on your fault, tell the vendor you want a Worcester fixed price repair at their expense, could be a few things but you will get a guarentee with their repair

 

[Alec_t]

tell the vendor you want a Worcester fixed price repair at their expense

If it was declared on the property information document, forming part of the conditions of sale, that the boiler/heating was working properly then you have a case against the vendor. Otherwise, it's a matter of 'buyer beware' AFAIK, so you wouldn't then be able to insist on repair at the vendor's expense.

 

[ianmcd]

If it was declared on the property information document, forming part of the conditions of sale, that the boiler/heating was working properly then you have a case against the vendor. Otherwise, it's a matter of 'buyer beware' AFAIK, so you wouldn't then be able to insist on repair at the vendor's expense.

As long as you inform your solicitor of the fault within 5 days from receiving the keys, then the vendor has to pay

 

[Aragorn84]

The pressure being high and the selection of the temp control knob would have no bearing whatsoever on your fault, tell the vendor you want a Worcester fixed price repair at their expense, could be a few things but you will get a guarentee with their repair

Yeah that was my feeling. The pressure was still well within the green range, so that was just a fob off. And the Temp control should be able to be set at any position without the boiler getting in a huff, and its not even as though its maxed out.

It behaved itself yesterday, but this morning it gave up again after i ran the bathroom sink. Same symptoms as before, water just begins to run warm and then goes cold, boiler gauge pegged at "U9". Additionally it seemed that it didnt start heating again. Despite the controls calling for heat, an hour later i went back to find the temp guage down in the low 20's and no heat output. I turned a tap on, and this time it correctly produced hot water, then afterwards resumed normal heating operation.

Will get back onto them.

 

[ianmcd]

The WB fixed price repair is really good value for money, the attending engineer loses their bonus if there is a call back, so will change everything that it could possibly be all for the one off cost

 

[Aragorn84]

Hmm, well the previous owner accepted my request and called WB, who sent out a local WB approved installer this morning. He looked it over, suggested it might be a blocked secondary HEX, and put some chemical flush into the system. He also said he was going to replace some temperature sensors though i didnt see him actually do this, hopefully he did. Hes coming back in two weeks to drain the flush out.

I must admit, i dont really buy their diagnosis. If it was a blocked HEX, it wouldnt have happily filled a bath, or run the shower for half an hour.

When the fault happens, its always at startup when you first turn on the tap or whatever.

 

[martyndc88]

It sounds like it's the pump, the older ones are prone to sticking intermittently.

 

[ianmcd]

A WB approved installer doesnt necessarily know anything about repairing their boilers, it just means he installs enough in a year to get that accolade

 

[Aragorn84]

A WB approved installer doesnt necessarily know anything about repairing their boilers, it just means he installs enough in a year to get that accolade

Yeah, so why send him out when you call the service helpline. I'm always this unlucky with trades. No matter how much research i do, i always end up with someone who doesnt do things properly.

I've stuck a camera on it so i can actually record the panel so i can see what exactly it does before and after it faults.

 

[Aragorn84]

It sounds like it's the pump, the older ones are prone to sticking intermittently.

Yeah, "pump" was my initial thought, given the symptoms of rapid overheat and kettling, but it threw me when it then runs the heating perfectly. And intermittent pump fault it could well be, but then, why does it only seem to fault in hot water mode?

 

[Aragorn84]

It sounds like it's the pump, the older ones are prone to sticking intermittently.

So on this point. It stopped again tonight and I couldn't get it to restart. I noticed something that probably does indeed point towards the pump.

When you switch the boiler off and back on at the button on the front panel, the pump fires up for a second or two. When it has faulted, each power cycle usually drops the temp by a bit and after a few goes it'll drop enough to start.

This evening at least half the times I cycled it, the pump did not run. When I eventually got it cooled enough it started up, heating only, no hot water at all, with the display flashing the Syphon fill symbol, and the temp climbed up into the 80s

A video showing what happened. Clearly, theres no water flow at all here, as siphon-fill runs at super low power. Heatings been off for hours and you would expect the temperature to plummet as soon as it starts pumping water, but instead it goes up.

I'll need to see if i can get them back out.

 

[Aragorn84]

Just to follow up, they swapped out the pump on Thursday. So far so good. No more oddness.

 

[Mattenstein]

A bit late here but I was reading through the replies about possibilities and rolling my eyes thinking 'just change the pump'! I've had that issue on 3 occasions with my British Gas branded Worcester Bosch boiler, where the display showed U9 and the boiler got really hot but provided no hot water, and on all 3 bloody occasions it was remedied by the pump being replaced. Luckily I have British Gas HomeCare and oddly enough the last time it happened, I already had an engineer on site to fix a leaky radiator!
Major installers push the WB boilers but based on my experience I agree with most independent installers on here, they're a bag of ****e.