Help Needed Please

[cr0ft]

Not often I'll ask for help but this one has stumped me. Working on a house with a combi-boiler system for a friend. Why do these things always happen when you do work for friends?

Simple job or so I thought, move the plumbing for the washing machine to the other side of the sink. Moved waste pipe easily. Drained down the cold system (and the hot as I had to remove a hot feed for the old machine too). Ran new pipework, filled and tested system. All good apart from one small problem - no hot water...

I've checked the combi-boiler. Water is definitely running to the boiler and all taps (hot and cold) are free of airlocks, i.e. water seems to flow smoothly.

The heating still works but not the hot water. Heating pressure is 1.2 bars at cold. I looked around the house and I can see potential airlock problems: -

1.) In the loft the riser mains still runs up to the loft before running 5 metres across the loft then back down around 2 metres to the boiler.
2.) The hot water pipework runs from the boiler up 3 feet or so prior to going straight through a wall then down around 2 feet under the floor on the other side (a cupboard).

Both of these would definitely airlock on a low pressure system. On a high pressure system could this be the problem? Is it possible that an airlock can allow a good flow to the taps but prevent the boiler from warming the water? The water does cycle from luke warm to cold so the boiler is trying to heat it but is cycling for whatever reason and never really getting warm.

A faulty diverter valve seems unlikely as the boiler worked fine before this draindown.

I could really use some advice from someone with more knowledge than I as this is a friend's house and I am feeling really bad right now, even though I know it's nothing I've directly done.

 

[Twinhawk]

so there is definatelty water running out of the hot tap but its not hot?

 

[Twinhawk]

only thing i can think off ,dont really work on combi boilers, any chance theres a check valve faulty on a hot applience which is also mains fed???

 

[cr0ft]

Definitely water running out of all the hot taps, very good flow rate (same as before she said). It cycles from cold to not so cold. The only thing I can think of that would need a check valve would be the thermostatic mixer shower in the bathroom. If this was faulty wouldn't this fault have been noticed before the draindown though? It seems too coincidental that this drain-down has brought on these symptoms.

Quite often I see shower installs where check valves aren't even fitted.

 

[Twinhawk]

it would quite possibly just be coincidental, however a few systems ive drained down rubber seals have become dry and leaked, not that a check valve has a rubber seal but worth isolating the shower if possible to check, it could be that the boiler isnt running correctly and after firing for a short while throws a fault and shuts itself off maybe pressure or gas flow, but i wouldnt know much about them, just started housy plumbing been on industrial sites untill......RESESSION

 

[cr0ft]

Hi and thanks. Is there anyone else with any ideas? I'm truly stumped on this. I wouldn't expect backflow as on a combi-boiler the hot and cold water pressures are going to be nearly balanced. Also, there's no where for the water to go except back into the water mains and that isn't going to happen as the pressure inside the house will be slightly lower than the mains pressure if anything.

 

[Avatar]

Sounds like a component in the boiler has gone - I do vented systems and the like, but combis are a speciailty in themselves - i think you need to call a heating engineer in to look at the boiler most likely.
At least that is what I would do.

Is the combi old? Often maintenance causes plumbing components to fail, that were operating previously . . .

Had the boiler been serviced yearly (i bet it hasn't!)

In which case it is your friends fault for not looking after it - call an expert in !

 

[Toddyplumb]

You are sure that when you moved wash machine pipework you have not crossed them ?

 

[cr0ft]

Just phoned them and they've tried throttling back the stopcock to reduce flow through the boiler. I thought it might be a flow rate problem as some older combis don't throttle back the hot water flow, they just pump out cold water if the flow rate is too high.

No luck.

I've got them to eliminate cross-flow from the kitchen mixer tap, shower mixer is service valved but the bath panel isn't easily removable so they can't easily check this but with balanced pressures I'm sure it's not the problem.

Definitely sure I haven't put the washing machine pipework in wrong although it's easily done! It was a case of removing the old runs and capping them and then putting a new cold feed off the kitchen sink pipework for the new one, no way to cross them over doing that!

This morning the boiler is not heating the hot water in the slightest whereas yesterday it was heating it a tiny bit and cycling from luke warm to cold. I think the problem has to be the boiler, it's just rubbish that this has come to light doing work for a friend!

Boiler is 7 years old and council fitted, not a brand I've heard of before either. I'm suspecting there is a component in the boiler that was just waiting to go 🙁

 

[Toddyplumb]

Sounds like boiler then

 

[Avatar]

Check it out!

 

[cr0ft]

It seems that the diverter valve has given up the ghost in the boiler. It was replaced for free by the council the following morning, but my question is how on earth could this be due to me draining down the cold/hot water system. The boiler was switched off during the draindown too.

 

[Bungditin]

Tends to be when the water mains is turned back on again and the valve becomes suddenly under pressure and the washer splits due to the force of the water.

 

[Billy Bob Bob]

i think you have crossed hot and cold,or thats what the symptoms suggest what make boiler?

 

[cr0ft]

All sorted, it was the diverted valve that the council replaced. Never had that happen before, will remember it for the future - another thing to add to the list of things to tell the customer 'may' happen before I start work!