Vaillant Combi Boiler

If it's not a 242 then disregard what I said - I had a 242 and it had the same symptoms as your combi, but I have no idea what your combi looks like inside, unless Vaillant use a largely common design. Ed Sirrett is a professional and has more of an idea than I do!

Andy.

When heating is on it takes an age to draw hot water. The diaphragm is new so what else could be the cause? The boiler is about 15-20 years old (VWSine).

Failed diverter valve. The diaphragm you refer to is presumably the HW flow sensor? I think they are sub £70 quid.

Tanks for the reply Andy. It is actually a VCW T3W (either 20/1, 25/1 or

(and the microswitch mentioned in Andy's post).

I used to have a Vaillant VCW25 Sine which did this! If yours is this type, You'll need to take off the front door, boiler 'stat knob, front panel and left hand side panel to get at the DHW flow switch, which is at the rear of the boiler, low down on the left, behind the "silver tank" which is the DHW heat exchanger. As another poster has said, the DHW flow switch operates a couple of microswitches which fire up the boiler when hot water (tap) is required.

In my case, the actuator rod had become very stiff through time and was hardly moving - thus no hot water. I cured it by squirting a small amount of WD40 at the point where the rod comes out of the flow switch body. You can get a pair of pliers onto the bar and move it up and down to get the WD40 to do its stuff. I then cleaned all the gunge off with paper towels, and a final short squirt of WD40 again. Never had any more problems after that.

HTH

Yep..that's the boiler. I will have a look at what you suggest tomorrow. Thanks.

WD40 really isn't the best long term fix

I would suggest silicone grease, until someone else picks me up on this

Maxie, you are right. WD40 is a water repellent NOT a lubricant.

Had this about 6 months ago and replaced the flow switch. I could not find a 'repair kit' though it looks a doddle to refurbish if I'd been able to do so. I got a new switch for around £105.

You could test whether it's a sluggish flow switch by removing the front cover, the cover of the switch box and lifting the switches with a long insulated screwdriver. It should fire up immediately.

Phil.

isn't the best long term fix

I'm not disagreeing with either of you - just telling what I did. I used the WD40 not to lube the actuator rod, but as a solvent to dissolve all of the crud and gunge which had accumulated through time.

It worked, and I never had any more problems in the further 13 years I lived at the house.

No problem - appreciate the reply

In message , IMM writes

Of course

Vaillants of this era are somewhat unique in their design features. I am very familiar with 242s this is a slightly earlier model called a Sine. It could be the diverter valve and the HW performance is still there at a reduced level because some water goes through the secondary heat exchanger. I rather assumed this might be the case.

This model has a cold/hot standby switch (this can make the difference of around 30 seconds for hot HW to arrive at the tap). It might be that the switch or some of the control gear has turned off this facility.

As you rightly say the DHW flow sensor whilst newly diaphragmed is sticky in some other way (this can certainly happen on 242s - but I don't know whether it's the same kit on Sines).

... further 13 years... we'd see a Puma,Ocean,Wickes etc. put in and removed during that time.

shut off all the radiator thermostats, plus, keep the cold/hot standby switchin the "instant" position if I am to guarantee hot water. This time of the year, with the heating on, if hot water is coming out of the tap and I turn the cold/hot standby switch into the other position (not instant) the boiler will shut off. To recap....in the summer with the rad switch off I can't get any hot water (most of the time). With the rad switch on I only get hot water if the standby switch is in the "instant" position. With the heating on, hot water takes up to 5 mins to come out of the tap and only then, with the standby switch in the "instant" position. I will never get hot water if the standby switch is not in the "instant" position. Perhaps it's time for a new boiler?

Obviously 90% of the kit is fine or you'd get no heating.

If this is a balanced flue model (IIRC Sines were also made with fanned flues) the there is something to be gained by replacing it. I strongly suspect that Vaillant will be bringing the prices of the Ecomax range down by a few hundred before next April else they won't be selling many boilers so you could wait till then if you can get it fixed.

Just tried this and no, with the instant hot water switch in the "off" position and hot tap running, the boiler will not fire up and there is no evidence of the pump running. If I switch to instant hot water whilst the tap is running the boiler will fire up no problem.

OK. The problem is definitely with the DHW flow sensor. This is a differential pressure type with a rubber diaphragm.

When you put the instant (hot standby) switch on the boiler fires because it is trying to preheat the innards, as you draw HW the preheating is thwarted and the boiler delivers HW after a fashion.